(Tbp  S.  1.  'Mi  ICtbrarg 


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M87 


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S00279059  W 


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APR  2  0 
h-NOV  '6  0  1983 


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NOV  1  8  m? 

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NOV  2  &  1994' 


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MAY  0  5  1??j 


5  1995 


DEC     3  »!**» 


, -tOOM/10-80 


SEX-LINKED  INHERITANCE  IN 

DROSOPHILA 


BY 


T.  H.  MORGAN  and  C.  B.  BRIDGES 


WASHINGTON 
Published  by  the  Carnegie  Institution  of  Washington 

1916 


M87 


^hr  D.  ii.  iitll  iCibrarji 


^'^rtll  Ctaruliua  ^VaU  llninrraita 


State  Library 


Gift  of 


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North  CarolWTflffillibWW 
Raleigh 

SEX-LINKED  INHERITANCE  IN 


DROSOPHILA 


/ 


BY 


T.  H.  MORGAN  and  C.  B.  BRIDGES 


WASHINGT 
Published  by  the  Carnegie  Insti 

1916 


THIS  BOOK  IS  DUE  ON  THE  DATE 
INDICATED  BELOW  AND  IS  SUB- 
JECT TO  AN  OVERDUE  FINE  AS 
POSTED  AT  THE  CIRCULATION 
DESK. 


FEB  2  0  1980 


MAfT^ 


1980 


\CQry 


NOV  2  c  1980 


mRTTWT 


<;nM/9.7B 


CARNEGIE  INSTITUTION  OF  WASHINGTON 
Publication  No.  237. 


^o,»$  of  thl$  800k 
•^»''e  rirst  issued 
IViAr8      1916 


PRESS  OP  GIBSON  BROTHERS,  INC. 
WASHINGTON,  D.  C. 


CONTENTS. 


PACE. 

Part  I.  Introductory S 

Mendel's  law  of  segregation 5 

Linkage  and  chromosomes 5 

Crossing-over 7 

The  Y  chromosome  and  non-disjunction ° 

Mutation  in  Drosophila  amfelophila ^° 

Multiple  allelomorphs " 

Sex-linked  lethals  and  the  sex  ratio H 

Influence  of  the  environment  on  the  realization  of  two  sex-linked  characters i6 

Sexual  polymorphism ^7 

Fertility  and  sterility  in  the  mutants '° 

Balanced  inviability " 

How  the  factors  are  located  in  the  chromosomes 20 

The  sex-linked  factors  of  Drosophila ^^ 

,  Map  of  chromosome  X 

Nomenclature * 

Part  II.  New  data ^5 

White ^5 

Rudimentary \ 

Mmiature 

Vermilion 

Yellow ^7 

Abnormal  abdomen ' 

r^     ■                                                                                                                        20 

Losm o 

Bifid •■•.•• ;,; f^ 

Linkage  of  bifid  with  yellow,  with  white,  and  with  vermilion Z9 

Linkage  of  cherry,  bifid,  and  vermilion 3° 

Reduplicated  legs ' 

Lethal  1 ^\ 

Lethal  \a 11 

Spot " 

Sable 34 

Linkage  of  yellow  and  sable 35 

Linkage  of  cherry  and  sable 37 

Linkage  of  eosin,  vermilion,  and  sable 37 

Linkage  of  miniature  and  sable + 

Linkage  of  vermilion,  sable,  and  bar + 

Dot ^ 

Linkage  of  vermilion  and  dot ** 

Bow f 

Bow  by  arc *^ 

Lemon  body-color •  • *„ 

Linkage  of  cherry,  lemon,  and  vermilion + 

Lethal  2 *^ 

Cherry ■ 

A  system  of  quadruple  allelomorphs •> 

Linkage  of  cherry  and  vermilion 5 

Compounds  of  cherry ^' 

Fused " 

Linkage  of  eosin  and  fused ^* 

Linkage  of  vermilion,  bar,  and  fused 5 

3 


4  CONTENTS. 

Part  II.  New  Data — Continued.  page. 

Forkfd rg 

Linkage  of  vermilion  and  forked eg 

linkaKt  of  cherry  and  forked eg 

Linkage  of  forked,  bar,  and  fused 60 

Linkage  of  sable,  rudimentary,  and  forked 61 

Linkage  of  rudimentary,  forked,  and  bar 62 

Shifted g. 

Linkage  of  shifted  and  vermilion 6^ 

Linkage  of  shifted,  vermilion,  and  bar 64 

Lethals  ja  and  sb g. 


Bar 


66 


^''"■-^-    ■ '.'.'.'.'.  66 

Depressed /r_ 

Linkage  of  depressed  and  bar 57 

Linkage  of  cherry,  depressed,  and  vermilion 68 

Club '.'.'.'.'.'.'.'.'.'.'..'.'. 69 

Gcnotypic  club _q 

Linkage  of  club  and  vermilion -q 

Lmkage  of  yellow,  club,  and  vermilion '    '  70 

Linkage  of  cherry,  club,  and  vermilion 72 

Green 

Chrome 

Lethal  3 ''^ 

Lethal  }a 74 

Lethal  lb '.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'..'. ^6 

Facet '' , 

Linkage  of  facet,  vermilion,  and  sable 

Lmkage  of  eosin,  facet,  and  vermilion ...  _o 

Lethal /f 7» 

Lethal  sd '.'.'.'.'.'.'.'.'.'.'.'.'.'.'. ''^ 

Furrowed '° 

.Additional  data  for  yellow,  white,  vermilion,  and  miniature 80 

New  data  contributed  by  A.  H.  Sturtevant  and  H.  J.  Muiler 82 

Summary  of  the  previously  determined  cross-over  values  g^ 

Summary  of  all  data  upon  linkage  of  gens  in  chromosome  I   c. 

Bibliography..  °4 

86 


PART  I.     INTRODUCTORY. 
MENDEL'S  LAW  OF  SEGREGATION. 

Although  the  ratio  of  3  to  i  in  which  contrasted  characters  reappear 
in  the  second  or  F2  generation  is  sometimes  referred  to  as  Mendel's  Law 
of  Heredity,  the  really  significant  discovery  of  Mendel  was  not  the 
3  to  I  ratio,  but  the  segregatio7i  of  the  characters  (or  rather,  of  the 
germinal  representatives  of  the  characters)  which  is  the  underlying 
cause  of  the  appearance  of  the  ratio.  Mendel  saw  that  the  characters 
with  which  he  worked  must  be  represented  in  the  germ-cells  by  specific 
producers  (which  we  may  call  factors),  and  that  in  the  fertilization  of 
an  individual  showing  one  member  of  a  pair  of  contrasting  characters 
by  an  individual  showing  the  other  member,  the  factors  for  the  two 
characters  meet  in  the  hybrid,  and  that  zvhen  the  hybrid  forms  germ-cells 
the  factors  segregate  frojn  each  other  zvithout  having  been  contaminated  one 
by  the  other.  In  consequence,  half  the  germ-cells  contain  one  member 
of  the  pair  and  the  other  half  the  other  member.  When  two  such 
hybrid  individuals  are  bred  together  the  combinations  of  the  pure  germ- 
cells  give  three  classes  of  offspring,  namely,  two  hybrids  to  one  of  each 
of  the  pure  forms.  Since  the  hybrids  usually  can  not  be  distinguished 
from  one  of  the  pure  forms,  the  observed  ratio  is  3  of  one  kind  (the 
dominant)  to  i  of  the  other  kind  (the  recessive). 

There  is  another  discovery  that  is  generally  included  as  a  part  of 
Mendel's  Law.  We  may  refer  to  this  as  the  assortment  in  the  germ-cells 
of  the  products  of  the  segregation  of  two  or  more  pairs  of  factors.  If 
assortment  takes  place  according  to  chance,  then  definite  Fo  ratios 
result,  such  as  9:3:3:1  (for  two  pairs)  and  27:9:9:9:3:3:3:1 
(for  three  pairs),  etc.  Mendel  obtained  such  ratios  in  peas,  and  until 
quite  recently  it  has  been  generally  supposed  that  free  assortment  is 
the  rule  when  several  pairs  of  characters  are  involved.  But,  as  we 
shall  try  to  show,  the  emphasis  that  has  been  laid  on  these  ratios  has 
obscured  the  really  important  part  of  Mendel's  discovery,  namely, 
segregation;  for  with  the  discovery  in  1906  of  the  fact  of  linkage  the 
ratios  based  on  free  assortment  were  seen  to  hold  only  for  combinations 
of  certain  pairs  of  characters,  not  for  other  combinations.  But  the 
principle  of  segregation  still  holds  for  each  pair  of  characters.  Hence 
segregation  remains  the  cardinal  point  of  Mendelism.  Segregation  is 
to-day  Mendel's  Law. 

LINKAGE  AND  CHROMOSOMES. 

It  has  been  found  that  when  certain  characters  enter  a  cross  together 
{i.  e.,  from  the  same  parent)  their  factors  tend  to  pass  into  the  same 
gamete  of  the  hybrid,  with  the  result  that  other  ratios  than  the 
chance  ratios  described  by  Mendel  are  found  in  the  Fo  generation. 

5 


6  SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 

Such  cases  of  linkage  have  been  described  in  several  forms,  but  no- 
where on  so  extensive  a  scale  as  in  the  pomace  fly,  Drosophila  ampelo- 
phila.  Here,  over  a  hundred  characters  that  have  been  investigated 
as  to  their  linkage  relations  are  found  to  fall  into  four  groups,  the 
members  of  each  group  being  linked,  in  the  sense  that  they  tend  to  be 
transmitted  to  the  gametes  in  the  same  combinations  in  which  they 
entered  from  the  parents.  The  members  of  each  group  give  free 
assortment  with  the  members  of  any  of  the  other  three  groups.  A 
most  significant  fact  in  regard  to  the  linkage  shown  by  the  Drosophila 
mutants  is  that  th^  number  of  linked  groups  corresponds  to  the  7iumber  of 
pairs  of  the  chromosomes.  If  the  gens  for  the  Mendelian  characters 
are  carried  by  the  chromosomes  we  should  expect  to  find  demonstrated 
in  Drosophila  that  there  are  as  many  groups  of  characters  that  are 
inherited  together  as  there  are  pairs  of  chromosomes,  provided  the 
chromosomes  retain  their  individuality.  The  evidence  that  the 
chromosomes  are  structural  elements  of  the  cell  that  perpetuate  them- 
selves at  every  division  has  continually  grown  stronger.  That  factors 
have  the  same  distribution  as  the  chromosomes  is  clearly  seen  in  the 
case  of  sex-linked  characters,  where  it  can  be  shown  that  any  character 
of  this  type  appears  in  those  individuals  which  from  the  known  distribu- 
tion of  the  X  cliromosomes  must  also  contain  the  chromosome  in  ques- 
tion. For  example,  in  Drosophila,  as  in  many  other  insects,  there  are 
two  X  chromosomes  in  the  cells  of  the  female  and  one  X  chromosome 
in  the  cells  of  the  male.  There  is  in  the  male,  in  addition  to  the  X,  also 
a  Y  chromosome,  which  acts  as  its  mate  in  synapsis  and  reduction. 
After  reduction  each  egg  carries  an  X  chromosome.  In  the  male  there 
are  two  classes  of  sperm,  one  carrying  the  X  chromosome  and  the  other 
carrying  the  Y  chromosome.  Any  egg  fertilized  by  an  X  sperm  pro- 
duces a  female;  any  egg  fertilized  by  a  Y  sperm  produces  a  male. 
I  he  scheme  of  mheritance  is  as  follows. 


The  sons  get  their  single  X  chromosome  from  their  mother,  and 
should  therefore  show  any  character  whose  gen  is  carried  by  such  a 
chromosome.  In  sex-jinked  inheritance  all  sons  show  the  characters 
of  their_mother^  A^maletransmits  his  sex-linked  character  tq^  his 
daughters,  who. show  it  if  dominant  ancl  conceal  it  Tf  recessive.  But 
any  daughter  will  transmit  such  a  character,  whether  dominant  or 
recessive,  to  half  of  her  sons.  The  path  of  transmission  of  the  gen 
is  the  same  as  the  path  followed  by  the  X  chromosome,  received  here 


INTRODUCTORY.  7 

from  the  male.  Many  other  combinations  show  the  same  relations. 
In  the  case  of  non-disjunction,  to  be  given  later,  there  is  direct  experi- 
mental evidence  of  such  a  nature  that  there  can  no  longer  be  any 
doubt  that  the  X  chromosomes  are  the  carriers  of  certain  gens  that 
we  speak  of  as  sex-hnked.  This  term  (sex-linked)  is  intended  to  mean 
that  such  characters  are  carried  by  the  X  chromosome.  It  has  been 
objected  that  this  use  of  the  term  implies  a  knowledge  of  a  factor  for 
sex  in  the  X  chromosome  to  which  the  other  factors  in  that  chromosome 
are  linked;  but  in  fact  we  have  as  much  knowledge  in  regard  to  the 
occurrence  of  a  sex  factor  or  sex  factors  in  the  X  chromosome  as  we 
have  for  other  factors.  It  is  true  we  do  not  know  whether  there  is 
more  than  one  sex-factor,  because  there  is  no  crossing-over  in  the 
male  (the  heterozygous  sex),  and  crossing-over  in  the  female  does  not 
influencethe  distribution  of  sex, since  like  parts  are  simplyinterchanged. 
It  follows  from  this  that  we  are  unable  as  yet  to  locate  the  sex  factor 
or  factors  in  the  X  chromosome.  The  fact  that  we  can  not  detect 
crossing-over  under  this  condition  is  not  an  argument  against  the 
occurrence  of  Hnkage.  We  are  justified,  therefore,  in  speaking  of  the 
factors  carried  by  the  X  chromosome  as  sex-linked. 

CROSSING-OVER. 

When  two  or  more  sex-linked  factors  are  present  in  a  male  they  are 
always  transmitted  together  to  his  daughters,  as  must  necessarily  be 
the  case  if  they  are  carried  by  the  unpaired  X  chromosome.  If  such 
a  male  carrying,  let  us  say,  two  sex-linked  factors,  is  mated  to  a  'w'ild 
female,  his  daughters  will  have  one  X  chromosome  containing  the 
factors  for  both  characters,  derived  from  the  father,  and  another  X 
chromosome  that  contains  the  factors  that  are  normal  for  these  two 
factors  (the  normal  allelomorphs).  The  sons  of  such  a  female  will  get 
one  or  the  other  of  these  two  kinds  of  chromosomes,  and  should  be 
expected  to  be  like  the  one  or  the  other  grandparent.  In  fact,  most 
of  the  sons  are  of  these  two  kinds.  But,  in  addition,  there  are  sons 
that  show  one  only  of  the  two  original  mutant  characters.  Clearly 
an  interchange  has  taken  place  between  the  two  X  chromosomes  in  the 
female  in  such  awaythat  a  piece  of  one  chromosome  hasbeen  exchanged 
for  the  homologous  piece  of  the  other.  The  same  conclusion  is  reached 
if  the  cross  is  made  in  such  awaythat  the  same  two  sex-linked  characters 
enter,  but,  one  from  the  mother  and  the  other  from  the  father.  1  he 
daughter  gets  one  of  her  sex  chromosomes  from  her  mother  and  the 
other  from  her  father.  She  should  produce,  then,  two  kinds  of  sons, 
one  like  her  mother  and  one  like  her  father.  In  fact,  the  majority  of 
her  sons  are  of  these  two  kinds,  but,  in  addition,  there  are  two  other 
kinds  of  sons,  one  kind  showing  both  mutant  characters,  the  other  kmd 
showing  normal  characters.  Here  again  the  results  must  be  due  to 
interchange  between  the  two  X's  in  the  hybrid  female.     The  number  oj 


8  SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 

the  sons  due  to  exchange  in  the  two  foregoing  crosses  is  ahvays  the  samey 
although  they  are  of  contrary  classes.  Clearly,  then,  the  interchange 
takes  place  irrespective  of  the  way  in  which  the  factors  enter  the  cross. 
W'c  call  those  classes  that  arise  through  interchange  between  the  chro- 
mosonus  "cross-over  classes"  or  merely  "cross-overs."  The  phenom- 
enon of  holding  together  we  speak,  of  as  linkage. 

I^v  taking  a  ninnher  of  factors  into  consideration  at  the  same  time 
it  has  been  shown  that  crossing-over  involves  large  pieces  of  the  chromo- 
somes. The  X  chromosomes  undergo  crossing-over  in  about  60  per 
cent  of  the  cases,  and  the  crossing-over  may  occur  at  any  point  along 
the  chromosome.  When  it  occurs  once,  whole  ends  (or  halves  even)  go 
over  together  and  the  exchange  is  always  equivalent.  If  crossing-over 
occurs  twice  at  the  same  time  a  middle  piece  of  one  chromosome  is 
intercalated  between  the  ends  of  the  other  chromosome.  This  process 
is  called  double  crossing-over.  It  occurs  not  oftener  than  in  about  10 
per  cent  of  cases  for  the  total  length  of  the  X  chromosome.  Triple 
crossing-over  in  the  X  chromosome  is  extremely  rare  and  has  been 
observed  only  about  a  half  dozen  times. 

\\  hile  the  genetic  evidence  forces  one  to  accept  crossing-over  between 
the  sex  chromosomes  in  the  female,  that  evidence  gives  no  clue  as  to 
how  such  a  process  is  brought  about.  There  are,  however,  certain 
facts  familiar  to  the  cytologist  that  furnish  a  clue  as  to  how  such  an 
interchange  might  take  place.  When  the  homologous  chromosomes 
come  together  at  synapsis  it  has  been  demonstrated,  in  some  forms  at 
least,  that  they  twist  about  each  other  so  that  one  chromosome  comes 
to  lie  now  on  the  one  side  now  on  the  other  of  its  partner.  If  at  some 
points  the  chromosomes  break  and  the  pieces  on  the  same  side  unite  and 
pass  to  the  same  pole  of  the  karyokinetic  spindle,  the  necessary  condi- 
tion for  crossing-over  will  have  been  fulfilled. 

THE  Y  CHROMOSOME  AND  NON-DISJUNCTION. 

Following  Wilson's  nomenclature,  we  speak  of  both  X  and  Y  as  sex 
chromosomes.  Both  the  cytological  and  the  genetic  evidence  shows 
that  when  two  X  chromosomes  are  present  a  female  is  produced,  when 
one,  a  male.  This  conclusion  leaves  the  Y  chromosome  without  any 
observed  relation  to  sex-determination,  despite  the  fact  that  the  Y  is 
normally  present  in  every  male  and  is  confined  to  the  male  line.  The 
question  may  be  asked,  and  in  fact  has  been  asked,  why  may  not  the 
presence  of  the  Y  chromosome  determine  that  a  male  develop  and  its 
absence  that  a  female  appear.^  The  only  answer  that  has  yet  been 
given,  outside  of  the  work  on  Drosophila,  is  that  since  in  some  insects 
there  is  no  '\'  chromosome,  there  is  no  need  to  make  such  an  assumption. 
But  in  Drosophila  direct  proof  that  Y  has  no  such  function  is  furnished 
by  the  evidence  discovered  by  Bridges  in  the  case  of  non-disjunction. 
(Bridges,  1913,  1914,  1916,  and  unpublished  results.) 


INTRODUCTORY.  9 

Ordinarily  all  the  sons  and  none  of  the  daughters  show  the  recessive 
sex-linked  characters  of  the  mother  when  the  father  carries  the  domi- 
nant allelomorph.  The  peculiarity  of  non-disjunction  is  that  some- 
times a  female  produces  a  daughter  like  herself  or  a  son  like  the 
father,  although  the  rest  of  the  offspring  are  perfectly  regular.  ¥ov 
example,  a  vermilion  female  mated  to  a  wild  male  produces  vermilion 
sons  and  wild-type  daughters,  but  rarely  also  a  vermilion  daughter 
or  a  wild-type  son.  The  production  of  these  exceptions  (primary 
exceptions)  by  a  normal  XX  female  must  be  due  to  an  aberrant  reduc- 
tion division  at  which  the  two  X  chromosomes  fail  to  disjoin  from  each 
other.  In  consequence  both  remain  in  the  egg  or  both  pass  into  the 
polar  body.  In  the  latter  case  an  egg  without  an  X  chromosome  is 
produced.  Such  an  egg  fertilized  by  an  X  sperm  produces  a  male  with 
the  constitution  XO.  These  males  received  their  single  X  from  their 
father  and  therefore  show  the  father's  characters.  While  these  XO 
males  are  exceptions  to  sex-linked  inheritance,  the  characters  that  they 
do  show  are  perfectly  normal,  that  is,  the  miniature  or  the  bar  or  other 
sex-linked  characters  that  the  XO  male  has  are  like  those  of  an  XY 
male,  showing  that  the  Y  normally  has  no  effect  upon  the  development 
of  these  characters.  But  that  the  Y  does  play  some  positive  role  is 
proved  by  the  fact  that  all  the  XO  males  have  been  found  to  be  abso- 
lutely sterile. 

While  the  presence  of  the  Y  is  necessary  for  the  fertility  of  the  male, 
it  has  no  effect  upon  sex  itself.  This  is  shown  even  more  strikingly  by 
the  phenomenon  known  as  secondary  non-disjunction.  If  the  two 
X  chromosomes  that  fail  to  disjoin  remain  in  the  egg,  and  this  egg  is 
fertilized  by  a  Y  sperm,  an  XXY  individual  results.  This  is  a  female 
which  is  like  her  mother  in  all  sex-linked  characters  (a  matroclinous 
exception),  since  she  received  both  her  X  chromosomes  from  her  mother 
and  none  from  her  father.  As  far  as  sex  is  concerned  this  is  a  perfectly 
normal  female.  The  extra  Y  has  no  effect  upon  the  appearance  of  the 
characters,  even  in  the  case  of  eosin,  where  the  female  is  much  darker 
than  the  male.  The  only  effect  which  the  extra  Y  has  is  as  an  extra 
wheel  in  the  machinery  of  synapsis  and  reduction;  for,  on  account  of 
the  presence  of  the  Y,  both  X's  of  the  XXY  female  are  sometimes  left 
within  the  ripe  egg,  a  process  called  secondary  non-disjunction.  In 
consequence,  an  XXY  female  regularly  produces  exceptions  (to  the 
extent  of  about  4  percent).  A  small  percentage  of  reductions  are  of 
this  XX-Y  type;  the  majority  are  X-XY.  The  XY  eggs,  produced  by 
the  X-XY  reductions,  when  fertilized  by  Y  sperm,  give  XYY  males, 
which  show  no  influence  of  the  extra  Y  except  at  synapsis  and  reduc- 
tion. By  mating  an  XXY  female  to  an  XYY  male,  XXYY  females 
have  been  produced  and  these  are  perfectly  normal  in  appearance. 
We  may  conclude  from  the  fact  that  visibly  indistinguishable  males 
have  been  produced  with  the  formulas  XO,  XY,  and  X\  "li ,  and  like- 


lO  SEX-MNKFD    INHKRITANCE    IN    DROSOPHILA. 

wise  ftniaks  with  the  formulas  XX,  XXY,  and  XXYY,  that  the  Y  is 
without  ert'cct  either  on  the  sex  or  on  the  visible  characters  (other  than 
fertility)  of  the  individual. 

The  evidence  is  equally  positive  that  sex  is  quantitatively  determined 
by  the  X  chromosome — that  twoX's  determine  a  female  and  one  a  male. 
For  in  the  case  of  non-disjunction,  a  zero  or  a  Y  egg  fertilized  by  an 
X  sperm  produces  a  male,  while  conversely  an  XX  egg  fertilized  by  a 
^'  sperm  produces  a  female.  It  is  thus  impossible  to  assume  that  the 
X  sperms  are  normally  female-producing  because  of  something  else 
than  the  X  or  that  the  Y  sperm  produce  males  for  any  other  reason 
than  that  they  normally  fertilize  X  eggs.  Both  the  X  and  the  Y  sperm 
have  been  shown  to  produce  the  sex  opposite  to  that  which  they 
normallv  produce  when  they  fertilize  eggs  that  are  normal  in  every 
respect,  except  that  of  their  X  chromosome  content.  These  facts 
establish  experimentally  that  sex  is  determined  by  the  combinations 
of  the  X  chromosomes,  and  that  the  male  and  female  combinations  are 
the  causes  of  sex  differentiation  and  are  not  simply  the  results  of  male- 
ness  and  femaleness  already  determined  by  some  other  agent. 

Cvtological  examination  has  demonstrated  the  existence  of  one 
XXY"\'  female,  and  has  checked  up  the  occurrence  in  the  proper 
classes  and  proportions  of  the  XXY  females.  Numerous  and  extensive 
breeding-tests  have  been  made  upon  the  other  points  discussed.  The 
evidence  leaves  no  escape  from  the  conclusion  that  the  genetic  excep- 
tions are  produced  as  a  consequence  of  the  exceptional  distribution  of 
the  X  chromosomes  and  that  the  gens  for  the  sex-linked  characters  are 
carried  by  those  chromosomes. 

MUTATION  IN  DROSOPHILA  AMPELOPHILA. 

The  first  mutants  were  found  in  the  spring  of  1910.  Since  then  an 
ever-increasing  series  of  new  types  has  been  appearing.  An  immense 
number  of  flies  have  come  under  the  scrutiny  of  those  who  are  working 
in  the  Zoological  Laboratory  of  Columbia  University,  and  the  discovery 
of  so  many  mutant  types  is  undoubtedly  due  to  this  fact.  But  that 
mutation  is  more  frequent  in  Drosophila  a^npelophila  than  in  some  of 
the  other  species  oi  Drosophila  seems  not  improbable  from  an  extensive 
examination  of  other  types.  It  is  true  a  few  mutants  have  been  found 
in  other  Drosophilas^  but  relatively  few  as  compared  with  the  number 
in  /).  ampdophila.  Whether  ampelophila  is  more  prone  to  mutate,  or 
whether  the  conditions  under  which  it  is  kept  are  such  as  to  favor  this 
process,  we  have  no  knowledge.  Several  attempts  that  we  have  made 
to  produce  mutations  have  led  to  no  conclusive  results. 

\  he  mutants  of  Drosophila  have  been  referred  to  by  Baur  as  "muta- 
tions through  loss,"  but  inasmuch  as  they  differ  in  no  respect  that  we 
can  discover  from  other  mutants  in  domesticated  animals  and  plants, 
there  is  no  particular  reason  for  putting  them  into  this  category  unless 


INTRODUCTORY.  I  I 

to  imply  that  new  characters  have  not  appeared,  or  that  those  that 
have  appeared  must  be  due  to  loss  in  the  sense  of  absence  of  something 
from  the  germ-plasm. 

In  regard  to  the  first  point,  several  of  the  mutants  are  characterized 
by  what  seem  to  be  additions.  For  example,  the  eye-color  sepia  is 
darker  than  the  ordinary  red.  At  least  three  new  markings  have  been 
added  to  the  thorax.  A  speck  has  appeared  at  the  base  of  the  wing,  etc. 
These  are  recessive  characters,  it  is  true,  but  the  character  "streak," 
which  consists  of  a  dark  band  added  to  the  thorax,  is  a  dominant.  If 
dominance  is  supposed  to  be  a  criterion  as  to  "  presence, "  then  it  should 
be  pointed  out  that  among  the  mutants  of  Drosophila  a  number  of 
dominant  types  occur.  But  clearly  we  are  not  justified  by  these  criteria 
in  inferring  anything  whatever  in  regard  to  the  nature  of  the  change 
that  takes  place  in  the  germ-plasm.  Probably  the  only  data  which 
give  a  basis  for  attempting  to  decide  the  nature  of  the  change  in  the 
germ-plasm  are  from  cases  where  multiple  allelomorphs  are  found. 
Several  such  cases  are  known  to  us,  and  two  of  these  are  found  in  the 
X  chromosome  group,  namely,  a  quadruple  system  (white,  eosin,  cherry, 
red),  and  a  triple  system  (yellow,  spot,  gray).  In  such  cases  each 
member  acts  as  the  allelomorph  of  any  other  member,  and  only  two 
can  occur  in  any  one  female,  and  only  one  in  any  male.  If  the  normal 
allelomorph  is  thought  of  as  the  positive  character,  which  one  of  the 
mutants  is  due  to  its  loss  or  to  its  absence?  If  each  is  produced  by  a 
loss  it  must  be  a  different  loss  that  acts  as  an  allelomorph  to  the  other 
loss.  This  is  obviously  absurd  unless  a  different  idea  from  the  one 
usually  promulgated  in  regard  to  "absence"  is  held. 

MULTIPLE  ALLELOMORPHS. 

It  appears  that  Cuenot  was  the  first  to  find  a  case  (in  mice)  in  which 
the  results  could  be  explained  on  the  basis  that  more  than  two 
factors  may  stand  in  the  relation  of  allelomorphs  to  each  other.  In 
other  words,  a  given  factor  may  become  the  partner  of  more  than  one 
other  factor,  although,  in  any  one  individual,  no  more  than  two  factors 
stand  in  this  relation.  While  it  appears  that  his  evidence  as  published 
was  not  demonstrative,  and  that,  at  the  time  he  wrote,  the  possibility 
of  such  results  being  due  to  very  close  linkage  could  not  have  been 
appreciated  as  an  alternative  explanation,  nevertheless  it  remains 
that  Cuenot  was  right  in  his  interpretation  of  his  results  and  that  the 
factors  for  yellow,  gray,  gray  white-belly,  and  black  in  mice  form  a 
system  of  quadruple  allelomorphs. 

There  are  at  least  two  such  systems  among  the  factors  in  the  first 
chromosome  in  Drosophila.  The  first  of  these  includes  the  factor  for 
white  eyes,  that  for  eosin  eyes,  and  that  for  cherry  eyes,  and  ol  course 
that  allelomorph  of  these  factors  present  in  the  wild  fly  and  which 
when  present  gives  the  red  color.     In  this  instance  the  normal  allelo- 


12  SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 

niorph  donun.itcs  all  the  other  three,  hut  in  mice  the  mutant  factor  for 
yellow  donunates  the  wild  or  "normal"  allelomorph. 

'Ihe  other  svstem  of  multiple  allelomorphs  in  the  first  chromosome  is 
a  tnple  system  made  up  of  yellow  (body-color),  spot  (on  abdomen), 
and  their  normal  allelomorph — the  factor  in  the  normal  fly  that  stands 

or     Kf'TV- 

In  general  it  may  be  said  that  there  are  two  principal  ways  in  which 
it  is  possible  to  show  that  certain  factors  (more  than  two)  are  the  allelo- 
morphs of  each  other.  First,  if  they  are  allelomorphs  only  two  can 
exist  in  the  same  individual;  and,  m  the  case  of  sex-linked  characters, 
while  two  ma\  exist  in  the  same  female,  only  one  can  exist  in  the  male, 
for  he  contains  but  one  X  chromosome.  Second,  all  the  allelomorphs 
should  pive  the  same  percentages  of  crossing-over  with  each  other  factor 
in  the  same  chromosome. 

It  is  a  question  of  considerable  theoretical  importance  whether  these 
cases  of  multiple  allelomorphs  are  only  extreme  cases  of  linkage  or 
whether  the\  form  a  system  (]uite  apart  from  linkage  and  in  relation  to 
normal  allelomorphism.  It  may  be  worth  while,  therefore,  to  discuss 
this  (juestion  more  at  length,  especially  because  Drosophila  is  one  of 
the  best  cases  known  for  such  a  discussion. 

I  he  factors  in  the  first  chromosome  are  linked  to  each  other  in  various 
degrees.  When  they  are  as  closely  linked  as  yellow  body-color  and 
white  eyes  crossing-over  takes  place  only  once  in  a  hundred  times.  If 
two  factors  were  still  nearer  together  it  is  thinkable  that  crossing-over 
might  be  such  a  rare  occurrence  that  it  would  require  an  enormous 
number  of  individuals  to  demonstrate  its  occurrence.  In  such  a  case 
the  factors  might  be  said  to  be  completely  linked,  yet  each  would  be 
supposed  to  have  its  normal  allelomorph  in  the  homologous  chromo- 
some of  the  wild  type.  Imagine,  then,  a  situation  in  which  one  of 
these  two  mutant  factors  (a)  enters  from  one  parent  and  the  other 
mutant  factor  (b)  from  the  other  parent.  The  normal  allelomorph  of 
a  may  be  called  A.  It  enters  the  combination  with  b,  while  the  normal 
allelomorph  R  of  b  enters  the  combination  with  a.  Since  b  is  completely 
linked  to  A  ami  a  to  B,  the  result  will  be  the  same  as  though  a  and  b 
were  the  allelomorphs  of  each  other,  for  in  the  germ-cells  of  the  hybrid 
aBAb  the  assortment  will  be  into  aB  and  Ab,  which  is  the  same  as 
though  a  and  b  acted  as  segregating  allelomorphs. 

I  here  is  no  way  from  Mendelian  data  by  which  this  difference 
between  a  true  caseof  multiple  allelomorphs  and  one  of  complete  linkage 
Lis  just  illustrated)  can  be  determined.  There  is,  however,  a  difl^erent 
line  of  attack  which,  in  a  case  like  that  o{ Drosophila,  will  give  an  answer 
to  this  question.  The  answer  is  found  in  the  way  in  which  the  mutant 
factors  arise.  This  argument  has  been  fully  developed  in  the  book 
entitled  "The  Mechanism  of  Mendelian  Inheritance,"  and  will  there- 
fore not  be  repeated  here.     It  must  suffice  to  say  that  if  two  mutant 


INTRODUCTORY.  1 3 

types  that  behave  as  allelomorphs  of  each  other  arise  separately  from 
the  wild  form,  one  of  them  must  have  arisen  as  a  double  mutation  of 
two  factors  so  close  to  each  other  as  to  be  completely  linked — a  highly 
improbable  occurrence  when  the  infrequency  of  mutations  is  taken  into 
consideration.^  The  evidence  opposed  to  such  an  interpretation  is 
now  so  strong  that  there  can  be  little  doubt  that  multiple  allelomorphs 
have  actually  appeared. 

On  a  priori  grounds  there  is  no  reason  why  several  mutative  changes 
might  not  take  place  in  the  same  locus  of  a  chromosome.  If  we  think 
of  a  chromosome  as  made  up  of  a  chain  of  chemical  particles,  there  may 
be  a  number  of  possible  recombinations  or  rearrangements  within  each 
particle.  Any  change  might  make  a  difference  in  the  end-product  of 
the  activity  of  the  cell,  and  give  rise  to  a  new  mutant  type.  It  is  only 
when  one  arbitrarily  supposes  that  the  only  possible  change  in  a  factor 
is  its  loss  that  any  serious  difficulty  arises  in  the  interpretation  of  mul- 
tiple allelomorphs. 

One  of  the  most  striking  facts  connected  with  the  subject  of  multiple 
allelomorphs  is  that  the  same  kind  of  change  is  effected  in  the  same 
organ.  Thus,  in  the  quadruple  system  mentioned  above,  the  color  of 
the  eye  is  affected.  In  the  yellow-spot  system  the  color  of  the  body  is 
involved.  In  mice  it  is  the  coat-color  that  is  different  in  each  member 
of  the  series.  While  this  is  undoubtedly  a  striking  relation  and  one 
which  seems  to  fit  well  with  the  idea  that  such  effects  are  due  to  muta- 
tive changes  in  the  same  fundamental  element  that  affects  the  char- 
acter in  question,  yet  on  the  other  hand  it  would  be  dangerous  to  lay 
too  much  emphasis  on  this  point,  because  any  given  organ  may  be 
affected  by  other  factors  in  a  similar  manner,  and  also  because  a  fac- 
tor frequently  produces  more  than  a  single  effect.  For  instance,  the 
factor  that  when  present  gives  a  white  eye  affects  also  the  general 
yellowish  pigment  of  the  body.  If  red-eyed  and  white-eyed  flies  are 
put  for  several  hours  into  alcohol,  the  yellowish  body-color  of  the 
white-eyed  flies  is  freely  extracted,  but  not  that  of  the  red-eyed  flies. 
In  the  living  condition  the  difference  between  the  body-colors  of  the 
red-  and  of  the  white-eyed  flies  is  too  slight  to  be  visible,  but  after 
extraction  in  alcohol  the  diflPerence  is  striking.  There  are  other  eflects 
also  that  follow  in  the  wake  of  the  white  factor.  Now,  it  is  quite 
conceivable  that  in  some  specific  case  one  of  the  eflFects  might  be  more 
striking  than  the  one  produced  in  that  organ  more  markedly  affected 
by  the  other  factor  of  the  allelomorphic  series.  In  such  a  case  the 
relation  mentioned  above  might  seemingly  disappear.  For  this  reason 
it  is  well  not  to  insist  too  strongly  on  the  idea  that  multiple  allelomorphs 
affect  the  same  part  in  the  same  way,  even  although  at  present  that 
appears  to  be  the  rule  for  all  known  cases. 

'For  a  fuller  discussion  see  "The  Mechanism  of  Mendelian  Heredity"  by  Morgan.  Sturtevant, 
Muller,  and  Bridges.     Henry  Holt  &  Co.,  1915. 


14  SEX-LIN  K.HD    INHERITANCE    IN    DROSOPHILA. 

SEX  LINKED  LETHALS  AND  THE  SEX  RATIO. 

Most  of  the  mutant  types  of  Drosophila  show  characteristics  that 
may  be  regarded  as  superficial  in  so  far  as  they  do  not  prevent  the 
animal  from  hving  in  the  protected  life  that  our  cultures  afford.  Were 
they  thrown  into  open  competition  with  wild  forms,  or,  better  said, 
were  thev  left  to  shift  for  themselves  under  natural  conditions,  many 
or  most  of  the  types  would  no  doubt  soon  die  out.  So  far  as  we  can  see, 
there  is  no  reason  to  suppose  that  the  mutations  which  can  be  described 
as  superficial  are  disproportionally  more  likely  to  occur  than  others. 
Of  course,  superficial  mutations  are  more  likely  to  survive  and  hence 
to  be  seen;  while  if  mutations  took  place  in  important  organs  some  of 
them  would  be  expected  to  affect  injuriously  parts  essential  to  the  Ufe 
of  the  individual  and  in  consequence  such  an  individual  perishes. 
The  "lethal  factors"  of  Drosophila  may  be  supposed  to  be  mutations 
of  some  such  nature;  but  as  yet  we  have  not  studied  this  side  of  the 
question  sufficiently,  and  this  supposed  method  of  action  of  the  lethals 
is  purely  speculative.  Whatever  the  nature  of  the  lethals'  action,  it 
can  be  shown  that  from  among  the  offspring  obtained  from  certain 
stocks  expected  classes  are  missing,  and  the  absence  of  these  classes 
can  be  accounted  for  on  the  assumption  that  there  are  present  mutant 
factors  that  follow  the  Mendelian  rule  of  segregation  and  which  show 
normal  linkage  to  other  factors,  but  whose  only  recognizable  difference 
from  the  normal  is  the  death  of  those  individuals  which  receive  them. 
The  numerical  results  can  be  handled  in  precisely  the  same  way  as 
are  other  linkage  results. 

There  are  some  general  relations  that  concern  the  lethals  that  may 
be  mentioned  here,  while  the  details  are  left  for  the  special  part  or  are 
found  in  the  special  papers  dealing  with  these  lethals.  A  factor  of  this 
kind  carried  by  the  X  chromosome  would  be  transmitted  in  the  female 
line  because  the  female,  having  two  X  chromosomes,  would  have  one  of 
them  with  the  normal  allelomorph  (dominant)  of  the  lethal  factor 
carried  by  the  other  X  chromosome.  Half  of  her  sons  would  get  one 
of  her  X's,  the  other  half  the  other.  Those  sons  that  get  the  lethal 
X  will  die,  since  the  male  having  only  one  X  lacks  the  power  of  con- 
taining both  the  lethal  and  its  normal  allelomorph.  The  other  half 
of  the  sons  will  survive,  but  will  not  transmit  the  lethal  factor.  In 
all  lethal  stocks  there  are  only  half  as  many  sons  as  daughters.  The 
heterozygous  lethal-bearing  female,  fertilized  by  a  normal  male,  will 
give  rise  to  two  kinds  of  daughters;  one  normal  in  both  X's,  the  other 
with  a  normal  X  and  a  lethal-bearing  X  chromosome.  The  former 
are  always  normal  in  behavior,  and  the  latter  repeat  in  their  descen- 
dants the  2  :  I  sex-ratio. 

\\  hether  a  female  bearing  the  same  lethal  twice  {i.e.,  one  homozygous 
for  a  given  lethal)  would  die,  can  not  be  stated,  for  no  such  females  are 
obtainable,  because  the  lethal  males,  which  alone  could  bring  about 


INTRODUCTORY.  I5 

such  a  condition,  do  not  exist.  The  presumption  is  that  a  female  of 
this  kind  would  also  die  if  the  lethal  acts  injuriously  on  some  vital 
function  or  structure. 

Since  only  half  of  the  daughters  of  the  lethal-bearing  females  carry 
the  lethal,  the  stock  can  be  maintained  by  breeding  daughters  separately 
in  each  generation  to  insure  obtaining  one  which  repeats  the  2  :  i  ratio. 
There  is,  however,  a  much  more  advantageous  way  of  carrying  on  the 
stock — one  that  also  confirms  the  sufficiency  of  the  theory. 

In  carrying  on  a  stock  of  a  lethal,  advantage  can  be  taken  of  linkage. 
A  lethal  factor  has  a  definite  locus  in  the  chromosome;  if,  then,  a 
lethal-bearing  female  is  crossed  to  a  male  of  another  stock  with  a  reces- 
sive character  whose  factor  lies  in  the  X  chromosome  very  close  to 
the  lethal  factor,  half  the  daughters  will  have  lethal  in  one  X  and  the 
recessive  in  the  other.  The  lethal-bearing  females  can  be  picked  out 
from  their  sisters  by  the  fact  that  they  give  a  2  :  i  sex-ratio,  and  by  the 
fact  that  nearly  all  the  sons  that  do  survive  showthe  recessive  character. 
If  such  females  are  tested  by  breeding  to  the  recessive  males,  then  the 
daughters  which  do  not  show  the  recessive  carry  the  lethal,  except  in 
the  few  cases  of  crossing-over.  Thus  in  each  generation  the  normal 
females  are  crossed  to  the  recessive  males  with  the  assurance  that  the 
lethal  will  not  be  lost.  If  instead  of  the  single  recessive  used  in  this 
fashion,  a  double  recessive  of  such  a  sort  that  one  recessive  lies  on  each 
side  of  the  lethal  is  used,  then  in  each  generation  the  females  which 
show  neither  recessive  will  almost  invariably  contain  the  lethal,  since 
a  double  cross-over  is  required  to  remove  the  lethal. 

It  is  true  that  females  carrying  two  different  lethals  might  arise  and 
not  die,  because  the  injurious  effect  of  each  lethal  would  be  dominated 
by  its  allelomorph  in  the  other  X  chromosome.  Such  females  can  not 
be  obtained  by  combining  two  existing  lethals,  since  lethal  males  do 
not  survive.  They  can  occur  only  through  a  new  lethal  arising  through 
mutation  in  the  homologous  chromosome  of  a  female  that  already 
carries  one  lethal.  Rare  as  such  an  event  must  be,  it  has  occurred  in 
our  cultures  thrice.  The  presence  of  a  female  of  this  kind  will  be  at 
once  noticed  by  the  fact  that  she  produces  no  sons,  or  very  rarely  one, 
giving  in  consequence  extraordinary  sex-ratios.  The  rare  appearance 
of  a  son  from  such  a  female  can  be  accounted  for  in  the  following  way: 
If  crossing-over  occurs  between  her  X  chromosomes  the  result  will  be 
that  one  X  will  sometimes  contain  two  lethals,  the  other  none.  The 
latter,  if  it  passes  into  a  male,  will  lead  to  the  development  of  a  normal 
individual.  The  number  of  such  males  depends  on  the  distance  apart 
of  the  two  lethals  in  the  chromosome.  There  is  a  crucial  test  ot  this 
hypothesis  of  two  lethals  in  females  giving  extraordinary  ratios.  This 
test  has  been  applied  to  the  cases  in  which  such  females  were  found, 
by  Rawls  (1913),  by  Morgan  (i9i4<:),  and  again  by  Stark  (191 5), 
and  it  has  been  found  to  confirm  the  explanation.     The  daughters  of 


l6  SEX-LINKEI)    INHERITANCE    IN    DROSOPHILA. 

such  n  fcmnle  shoiiki  all  (exceprin-i;  a  rare  one  due  to  crossing-over) 
mvf  2  :  1  ratios,  because  each  daughter  must  get  one  or  the  other  X 
chromosome  of  her  mother,  that  is,  one  or  the  other  lethal.  Although 
the  mother  was  fertilized  by  a  normal  male,  every  daughter  is  hetero- 
zygous for  one  or  the  other  of  the  lethal  factors.  The  daughters  of  the 
two-lethal  females  differ  from  the  daughters  of  the  one-lethal  female  in 
that  the  former  mother,  as  just  stated,  gives  all  lethal-bearing  daughters; 
tin-  latter  transmits  her  lethal  to  only  half  of  her  daughters. 

INFLUENCE  OF  THE  ENVIRONMENT  ON  THE  REALIZATION  OF  TWO 

SEX-LINKED  CHARACTERS. 

The  need  of  a  special  environment  in  order  that  certain  mutant 
characters  may  express  themselves  has  been  shown  for  abnormal 
abdomen  (Morgan,  191 2r/,  191 5/^)  and  for  reduplication  of  the  legs 
(Hoge,  191 5).  In  a  third  type,  club,  described  here  (page  69),  the 
failure  of  the  unfolding  of  the  wing  which  occurs  in  about  20  per  cent 
of  the  flies  is  also  without  much  doubt  an  environmental  effect,  but  as 
yet  the  particular  influence  that  causes  the  change  is  unknown. 

A  very  extensive  series  of  observations  has  been  made  on  the  char- 
acter called  abnormal  abdomen.  In  pure  cultures  kept  moist  with 
abundance  of  fresh  food  all  the  flies  that  hatch  for  the  first  few  days 
have  the  black  bands  of  the  abdomen  obliterated  or  made  faint  and 
irregular.  As  the  bottles  get  dry  and  the  food  becomes  scarce  the  flies 
become  more  and  more  normal,  until  at  last  they  are  indistinguishable 
from  the  normal  flies.  Nevertheless  these  normal-looking  flies  will  give 
rise  in  a  suitable  environment  to  the  same  kind  of  flies  as  the  very 
abnormal  flies  first  hatched.  By  breeding  from  the  last  flies  of  each 
culture,  and  m  dry  cultures,  flies  can  be  bred  from  normal  ancestors  for 
several  generations,  and  then  by  making  the  conditions  favorable  for 
the  appearance  of  the  abnormal  condition,  the  flies  will  be  as  abnormal 
as  though  their  ancestors  had  always  been  abnormal.  Here,  then,  is  a 
character  that  is  susceptible  to  the  variations  in  the  environment,  yet 
whatever  the  realized  condition  of  the  soma  may  be,  that  condition 
has  no  eflfect  whatever  on  the  nature  of  the  germ-plasm.  A  more 
striking  disproof  of  the  theory  of  the  inheritance  of  acquired  characters 
would  be  hard  to  find. 

A  demonstration  is  given  in  this  instance  of  the  interaction  between 
a  given  genotypic  constitution  and  a  special  environment.  The  char- 
acter abnormal  is  a  sex-linked  dominant.  Therefore,  if  an  abnormal 
male  is  mated  to  a  wild  female  the  daughters  are  heterozygous  for 
abnormal,  while  the  sons,  getting  their  X  chromosome  from  their 
mother,  are  entirely  normal.  In  a  wet  environment  all  the  daughters 
are  abnormal  and  the  sons  normal.  As  the  culture  dries  out  the 
daughters'  color  becomes  normal  in  appearance.     But  while  the  sons 


Kaleigh 

INTRODUCTORY.  I 7 

will  never  transmit  abnormality  to  any  of  their  descendants  in  any 
environment,  the  daughters  will  transmit  (if  bred  to  normal  males)  in 
a  suitable  environment  their  peculiarity  to  half  of  their  daughters  and 
to  half  of  their  sons.  The  experiment  shows  convincingly  that  the 
abnormal  abdomen  appears  in  a  special  environment  only  in  those  flies 
that  have  a  given  genotypic  constitution. 

As  the  cultures  dry  out  the  abnormal  males  are  the  first  to  change 
over  to  normal,  then  the  heterozygous  females,  and  lastly  the  homo- 
zygous females.  It  is  doubtful  if  any  far-reaching  conclusion  can  be 
drawn  from  this  series,  because  the  first  and  second  classes  differ  from 
each  other  not  only  in  the  presence  of  one  or  of  two  factors  for  abnor- 
mal, but  also  by  the  absence  in  the  first  case  (male)  of  an  entire  X 
chromosome  with  its  contained  factors.  The  second  and  third  classes 
differ  from  each  other  only  by  the  abnormal  factor. 

Similar  results  were  found  in  the  mutant  type  called  reduplicated 
legs,  which  is  a  sex-linked  recessive  character  that  appears  best  when 
the  cultures  are  kept  at  about  10°  C.  As  Miss  M.  A.  Hoge  has  shown, 
this  character  then  becomes  realized  in  nearly  all  of  the  flies  that  have 
the  proper  constitution,  but  not  in  flies  of  normal  constitution  placed 
in  the  same  environment.     Here  the  effect  is  produced  by  cold. 

SEXUAL  POLYMORPHISM. 

Outside  the  primary  and  secondary  sexual  differences  between  the 
male  and  the  female,  there  is  a  considerable  number  of  species  of 
animals  with  more  than  one  kind  of  female  or  male.  Darwin  and  his 
followers  have  tried  to  explain  such  cases  on  the  grounds  that  more 
than  one  kind  of  female  (or  male)  might  arise  through  natural  selection, 
in  consequence  of  some  individuals  mimicking  a  protected  species.  It 
is  needless  to  point  out  here  how  involved  and  intricate  such  a  process 
would  be,  because  the  mutation  theory  has  cut  the  Gordian  knot 
and  given  a  simpler  solution  of  the  origin  of  such  diandromorphic  and 
digynomorphic  conditions. 

In  Drosophila  a  mut,ant,  eosin  eye-color,  appeared  in  which  the 
female  has  darker  eyes  than  the  male.  If  such  stock  is  crossed  with 
cherry  (another  sex-linked  recessive  mutant,  allelomorphic  to  eosin) 
the  females  in  the  F2  generation  are  alike  (for  the  pure  eosin  and  the 
eosin-cherry  compound  are  not  separable),  but  the  cherry  males  and 
the  eosin  males  are  quite  different  in  appearance.  Here  we  have  a  simu- 
lation, at  least,  of  a  diandromorphic  species.  Such  a  group  perpetuates 
itself,  giving  one  type  of  female  (inasmuch  as  eosin  and  cherry  females 
are  very  closely  similar)  and  two  types  of  males,  only  one  of  which  is 
like  the  females.  A  population  of  this  kind  is  very  directly  comparable 
to  certain  polymorphic  types  that  occur  in  nature.  In  Colias  phdodtce 
there  is  one  type  of  male,  yellow,  and  two  types  of  females,  yellow  and 


l8  SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 

w  hitf.  In  Colias  nirydice  the  male  is  orange  and  the  females  are  orange 
or  white.  In  Papilio  turnus  the  male  is  yellow  and  the  females  either 
yellow  or  black.  Those  cases  are  directly  comparable  to  an  eosin- 
cherry  population,  except  that  in  Lepidoptera  the  female  is  heterozy- 
gous for  the  sc.\  differential,  in  Diptera  the  male. 

Since  in  Drosophila  the  results  are  explicable  on  a  sex-linked  basis, 
a  similar  explanation  may  apply  to  polymorphism  in  butterflies.  By 
suitable  combinations  of  eosin  and  cherry  most  of  the  cases  of  poly- 
morphism in  butterflies  may  be  simulated.  To  simulate  the  more 
complex  cases,  such  as  that  of  Papilio  polytes  and  memnon,  another 
allelomorph  like  eosin  would  have  to  be  introduced.  A  population  of 
mixed  cherry  and  white  would  give  three  somatic  types  of  females 
^cherry,  cherry-white,  and  white)  and  two  of  males  (cherry  and  white). 

FERTILITY  AND  STERILITY  IN  THE  MUTANTS. 

Aside  from  the  decrease  in  fertility  that  occurs  in  certain  stocks 
(a  question  that  need  not  be  treated  here),  there  are  among  the  types 
described  in  the  text  two  cases  that  call  for  special  comment.  When 
the  mutant  type  called  "rudimentary"  was  first  discovered,  it  was 
found  that  the  females  were  sterile  but  the  males  were  fully  fertile. 
Later  work  has  revealed  the  nature  of  the  sterility  of  the  female.  The 
ovaries  are  present  and  in  the  young  flies  appear  normal,  but  while  in 
the  normal  flies  the  eggs  in  the  posterior  portion  enlarge  rapidly  during 
the  first  few  days  after  hatching,  in  the  rudimentary  females  only  a 
very  few  (about  15)  eggs  enlarge.  The  other  eggs  in  the  ovary  remain 
at  a  lower  stage  of  their  development.  Rarely  the  female  lays  a  few 
eggs;  when  she  does  so  some  of  the  eggs  hatch,  and  if  she  has  been 
mated  to  a  rudimentary  male,  the  oflFspring  are  rudimentary  females 
and  males.  The  rudimentary  females  mate  in  the  normal  time  with 
rudimentary  or  with  normal  males,  and  their  sexual  behavior  is  normal. 
Tiuir  sterility  is  therefore  due  to  the  failure  of  the  eggs  to  develop 
properly.  Whether  in  addition  to  this  there  is  some  incompatibility 
between  the  sperm  and  the  eggs  of  this  type  (as  supposed  to  be  the  case 
at  one  time)  is  not  conclusively  disproved,  but  is  not  probable  from  the 
evidence  now  available. 

In  the  mutant  called  "fused"  the  females  are  sterile  both  with  wild 
males  and  with  males  from  their  own  stock.  An  examination  of  the 
ovaries  of  these  females,  made  by  Mr.  C.  McEwen,  shows  clearly  that 
tiure  are  fewer  than  the  normal  number  of  mature  eggs,  recalling  the 
case  of  rudimentary. 

It  should  be  noticed  that  there  is  no  apparent  relation  between  the 
sterility  of  these  two  types  and  the  occurrence  of  the  mutation  in  the 
X  chromosome,  because  other  mutations  in  the  X  do  not  cause  sterility, 
and  there  is  sterility  in  other  mutant  types  that  are  due  to  factors  in 
other  chromosomes. 


INTRODUCTORY. 


19 


BALANCED  INVIABILITY. 

The  determination  of  the  cross-over  values  of  the  factors  was  at  Hrst 
hindered  because  of  the  poor  viabihty  of  some  of  the  mutants.  If  the 
viabiHty  of  each  mutant  type  could  be  determined  in  relation  to  the 
viability  of  the  normal,  "coefficients  of  viability"  could  serve  as  cor- 
rections in  working  with  the  various  mutant  characters.  But  it  was 
found  (Bridges  and  Sturtevant,  1914)  that  viability  was  so  erratic  that 
coefficients  might  mislead.  At  the  same  time  it  was  becoming  more 
apparent  that  poor  viability  is  no  necessary  attribute  of  a  character, 
but  depends  very  largely  on  the  condition  of  culture.  Competition 
among  larvae  was  found  to  be  the  chief  factor  in  viability.  Mass 
cultures  almost  invariably  have  extremely  poor  viability,  even  though 
an  attempt  is  made  to  supply  an  abundance  of  food.  Special  tests 
(Morgan  and  Tice,  1914)  showed  that  even  those  mutants  which  w^ere 
considered  the  very  poorest  in  viability  were  produced  in  proportions 
fairly  close  to  the  theoretical  when  only  one  female  was  used  for  each 
large  culture  bottle  and  the  amount  and  quality  of  food  was  carefully 
adjusted. 

For  the  majority  of  mutants  which  did  well  even  under  heavy  com- 
petition in  mass  cultures  the  pair-breeding  method  reduced  the  dis- 
turbances due  to  viability  to  a  point  where  they  were  negligible. 

Later  a  method  was  devised  (Bridges,  1915)  whereby  mutations  of 
poor  viability  could  be  worked  with  in  linkage  experiments  fairly  accu- 
rately and  whereby  the  residual  inviability  of  the  ordinary  characters 
could  be  largely  canceled.  This  method  consists  in  balancing  the 
data  of  a  certain  class  with  poor  viability  by  means  of  an  equivalent 
amount  of  data  in  which  the  same  class  occurs  as  the  other  member  of 
the  ratio.  Thus  in  obtaining  data  upon  any  linkage  case  it  is  best  to 
have  the  total  number  of  individuals  made  up  of  approximately  equal 
numbers  derived  from  each  of  the  possible  ways  in  which  the  experiment 
may  be  conducted.  In  the  simplest  case,  in  which  the  results  are  of 
the  form  AB  :  Ab  :  aB  :  ab,  let  us  suppose  that  the  class  ab  has  a  dis- 
proportionately low  viability.  If,  then,  ab  occurs  in  an  experiment  as  a 
cross-over  class,  that  class  will  be  too  small  and  a  false  linkage  value 
will  be  calculated.  The  remedy  is  to  balance  the  preceding  data  by 
an  equal  amount  of  data  in  which  ab  occurs  as  a  non-cross-over.  In 
these  latter  the  error  will  be  the  opposite  of  the  previous  one,  and 
by  combining  the  two  experiments  the  errors  should  be  balanced  to 
give  a  better  approximation  to  the  true  value.  When  equal  amounts  of 
data,  secured  in  these  two  ways,  are  combined,  all  four  classes  will  be 
balanced  in  the  required  manner  by  occurring  both  as  non-cross-overs 
and  as  cross-overs.  The  error,  therefore,  should  be  very  small,  tor 
three  pairs  of  gens  there  are  eight  classes,  and  in  order  that  each  ot 
them  may  appear  as  a  non-cross-over,  as  each  single  cross-over,  and  as 
the  double  cross-over,  four  experiments  must  be  made. 


20  SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 

HOW  THE  FACTORS  ARE  LOCATED  IN  THE  CHROMOSOMES. 

A  character  is  in  the  first  chromosome  if  it  is  transmitted  by  the 
grandfather  to  half  of  his  grandsons,  while,  in  the  reciprocal  cross,  the 
mother  transmits  her  character  to  all  her  sons  (criss-cross  inheritance) 
and  to  half  of  her  granddaughters  and  to  half  of  her  grandsons;  in 
other  words,  if  the  factor  that  differentiates  the  character  has  the  same 
distribution  as  the  X  chromosome.  If,  however,  a  new  mutant  type 
does  not  show  this  sex-linked  inheritance,  its  chromosome  is  determined 
by  taking  advantage  of  the  fact  that  in  Drosophila  there  is  no  crossing- 
over  in  the  male  between  factors  in  the  same  chromosome.  For 
instance,  if  a  new  mutant  type  is  found  not  to  be  sex-linked,  its  group 
is  determined  by  the  following  tests :  It  is  crossed  to  black,  whose  factor 
is  known  to  be  in  the  second  chromosome,  and  to  pink,  whose  factor 
lies  in  the  third  chromosome.  If  the  factor  of  the  new  form  should 
happen  to  be  in  the  second  chromosome,  then,  in  the  cross  with  black, 
no  double  recessive  can  appear,  so  that  the  F2  proportion  is  2:1:1:0; 
but  with  pink,  the  mutant  type  should  give  the  proportion  9:3:3:1, 
typical  of  free  assortment. 

If,  however,  the  factor  of  the  new  form  is  in  the  third  chromosome, 
then,  when  crossed  to  black,  the  double  recessive  and  the  9:3:3:1 
proportion  appear  in  Fo.  But  wMien  crossed  to  pink  no  double  recessive 
appears  in  F;.,  and  the  proportion  2:1:1:0  occurs. 

If  these  tests  show  that  the  new  mutant  does  not  belong  to  either  the 
second  or  third  chromosome,  that  is,  it  both  with  black  and  with  pink 
the  9:3:3:1  ratio  is  obtained,  then  by  exclusion  the  factor  lies  in  the 
fourth  chromosome,  in  which  as  yet  only  two  factors  have  been  found. 

We  propose  to  give  in  a  series  of  papers  an  account  of  the  mutant 
races  of  Drosophila  and  the  linkage  shown  in  their  inheritance.  In  this 
paper  we  shall  consider  only  the  members  of  the  first  chromosome, 
descnbmg  a  large  number  of  new  mutants  with  their  linkage  relations 
and  summarizing  to  date  all  the  linkage  data  relating  to  the  first 
chromosome.  In  later  papers  we  propose  to  consider  the  members 
of  the  second,  third,  and  fourth  chromosomes. 

The  list  at  the  top  of  page  21  gives  the  names  of  the  factors  dealt 
with  111  this  paper.  They  stand  in  the  order  of  their  discovery,  the 
mutant  forms  reported  here  for  the  first  time  being  starred. 

In  each  experiment  the  percentage  of  crossing-over  is  found  by 
dividing  the  number  of  the  cross-overs  by  the  sum  of  the  non-cross- 
overs and  the  cross-overs,  and  multiplying  this  quotient  by  100.  The 
resultmg  percentages,  or  cross-over  values,  are  used  as  measures  of  the 
distances  between  loci.  Fhus  if  the  experiments  give  a  cross-over 
value  of  5  per  cent  for  white  and  bifid,  we  say  that  white  and  bifid  lie  5 
units  apart  in  the  X  chromosome.  Other  experiments  show  that  yellow 
and  white  are  about  i  unit  apart,  and  that  yellow  and  bifid  are  about 
6  units  apart.     We  can  therefore  construct  a  diagram  with  yellow  as 


INTRODUCTORY. 


21 


The  sex-linked  factors  of  Drosophila. 


Gen. 


White 

Rudimentary 
Miniature.  .  . 
Vermilion.  .  . 

Yellow 

Abnormal .  .  . 

Eosin 

Bifid 

Reduplicated 

Lethal  1 

Lethal  la*.  .  . 

Spot* 

Sable* 

Dot* 

Bow* 

Lemon* 

Lethal  2 

Cherry 

Fused* 

Forked* 

Shifted* 

Lethal  sa. . . . 

Bar 

Notch 

Depressed*  .  . 
Lethal  sb. .  .  . 

Club* 

Green* 

Chrome* .... 

Lethal  3 

Lethal  3a. .  .  . 
Lethal li*... 

Facet* 

Lethal  sc .  .  .  . 
Lethal sd. .  .  . 
Furrowed. . . . 


Part  affected. 


Eye-color. . . 

Wings 

Wings 

Eye-color. . . 
Body-color. 
Abdomen. . . 
Eye-color. . . 

Wings 

Legs 

Life 

Life 

Body-color. 
Body-color . 

Thorax 

Wings 

Body-color . 

Life 

Eye-color. . . 
Venation .  .  . 
Bristles.  .  .  . 
Venation .  .  . 

Life 

Eye-shape. . 

Wing 

Wing 

Life 

Wings 

Body-color.  . 
Body-color.  . 

Life 

Life 

Life 

Eye 

Life 

Life 

Eye 


Figure 


II 
A 

7-8 

lO 

5 

4 

7-8 

B 


14-17 

2 


C 

3 


9 
D 

E 
F 


12-13 


H 


Symbol. 


r 
m 

V 

y 

A' 

we 

bi 


h 

ha 

ys 
s 


Im 

•2 
WC 

fu 

f 

Sh 
Isa 

B' 

N' 
dp 

isb 
Cf 


I3 

I16 

fa 

Isc 

Isd 
fw 


^ocus. 


I .  I 

55-1 
36.1 
33.0 

0.0 

2.4 

I . 

6. 

34- 
o. 

3. 
o. 

43- 
33 


I 

■3 
■7 
■7 
■3 
.0 
.0 


175 
12.5  = 

I .  I 

59-5 
56. 5 
17.8 
23.7 
57. o 
2.6 
18.0 
16.7 
14.6 


26.5 

195 
I 

2.2 

66.2 


I  — 


38. 


Datef 

ound. 

May 

1910 

June 

1910 

Aug. 

1910 

Nov. 

1910 

Jan. 

1911 

July 

1911 

Aug. 

1911 

Nov. 

1911 

Nov. 

1911 

Feb. 

1912 

Mar. 

1912 

April 

1912 

July 

1912 

July 

1912 

Aug. 

1912 

Aug. 

1912 

Sept. 

1912 

Oct. 

[912 

Nov. 

1912 

Nov. 

[912 

Jan. 

1913 

Jan. 

913 

Feb. 

913 

Mar. 

913 

.April 

913 

April  1 

913 

May  1 

913 

May  1 

913 

Sept.  1 

913 

Dec.  1 

913 

Jan.    1 

914 

Feb.   1 

914 

Feb.   1 

914 

April  1 

914 

May  1 

914 

Nov.  1 

914 

Found  by. 


Morgan. 

Morgan. 

Morgan. 

Morgan. 

Wallace. 

Morgan. 

Morgan. 

Morgan. 

Hoge. 

Rawls. 

Rawls. 

Cattell. 

Bridges. 

Bridges. 

Bridges. 

Wallace. 

Morgan. 

Safir. 

Bridges. 

Bridges. 

Bridges. 

Stark. 

Tice. 

Dexter. 

Bridges. 

Stark. 

Morgan. 

Bridges. 

Bridges. 

Morgan. 

Morgan 

Morgan. 

Bridges. 

Stark. 

Stark. 

Duncan. 


the  zero,  with  white  at  i,  and  with  bifid  at  6.  If  we  know  the  cross- 
over values  given  by  a  new  mutant  with  any  two  mutants  of  the  same 
chromosome  whose  positions  are  already  determined,  then  we  can 
locate  the  new  factor  with  accuracy,  and  be  able  to  predict  the  cross- 
over value  which  the  new  factor  will  give  with  any  other  factor  whose 
position  is  plotted. 

The  factors  are  located  preferably  by  short  distances  (i.  e.,  by  those 
cases  in  which  the  amount  of  crossing-over  is  small),  because  when  the 
amount  of  crossing-over  is  large  a  correction  must  be  made  for  double 
crossing-over,  and  the  correction  can  be  best  found  through  breaking  up 
the  long  distances  into  short  ones,  by  using  intermediate  pomts. 

Conversely,  when  a  long  distance  is  indicated  on  the  chromosome 
diagram,  the  actual  cross-over  value  found  by  experiment  (;.  e.,  the 


SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 


6.3       -  -       Bifid 


12.5       -  ■ 

M.G       -  - 

10.7 
17.5 
17.8 
18.0 
19.5 


23.7 


26.5 


YeUoat,  spot 

thai  I 
Lethal  lb 
■Whilg.  eosin,  cherry 


Facet 
Alinormal 
Notch 
Lethal  la 


33.0 
33.± 

34.7 

36.1 


Lethal  II 

l^ethal  sb 

Club 
Lemon 
Shifted 
Depressed 
Lethal  Ilia 


Lethal  sa 
Lethal  III 


•  Vermilion 
Dot 

Reduplicated 
Miniature 


38.0       -  -       Furrowed 


43.0       -  -       Sable 


55.1 
57.0 
.59.5 


Rudimentary 

Forked 
Bar 


Fused- 


66.2       -  -      Lethal  sc 


Diagram  I. 


INTRODUCTORY. 


23 


percentage  of  cross-overs)  will  be  less  than  the  diagram   indicates, 
because  the  diagram  has  been  corrected  for  double  crossing-over. 

Diagram  I  has  been  constructed  upon  the  basis  of  all  the  data  sum- 
marized in  table  65  (p.  84)  for  the  first  or  X  chromosome.  It  shows  the 
relative  positions  of  the  gens  of  the  sex-linked  characters  oi  Drosophila. 
One  unit  of  distance  corresponds  to  i  per  cent  of  crossing-over.  Since 
all  distances  are  corrected  for  double  crossing-over  and  for  coincidence, 
the  values  represent  the  total  of  crossing-over  between  the  loci.  The 
uncorrected  value  obtained  in  any  experiment  with  two  loci  widely- 
separated  will  be  smaller  than  the  value  given  in  the  map. 

It  may  be  asked  what  will  happen  when  two  factors  whose  loci  are 
more  than  50  units  apart  in  the  same  chromosome  are  used  in  the  same 
experiment?  One  might  expect  to  get  more  than  50  per  cent  of  cross- 
overs with  such  an  experiment,  but  double  crossing-over  becomes  dis- 
proportionately greater  the  longer  the  distance  involved,  so  that  in 
experiments  the  observed  percentage  of  crossing-over  does  not  rise 
above  50  per  cent.  For  example,  if  eosin  is  tested  against  bar,  some- 
what under  50  per  cent  of  cross-overs  are  obtained,  but  if  the  distance  of 
bar  from  eosin  is  found  by  summation  of  the  component  distances  the 
interval  for  eosin  bar  is  56  units. 

In  calculating  the  loci  of  the  first  chromosome,  a  system  of  weighting 
was  used  which  allowed  each  case  to  influence  the  positions  of  the  loci 
in  proportion  to  the  amount  of  the  data.  In  this  way  advantage  was 
taken  of  the  entire  mass  of  data. 

The  factors  (lethal  i,  white,  facet,  abnormal,  notch,  and  bifid)  which 
lie  close  to  yellow  were  the  first  to  be  calculated  and  plotted.  Ihe 
next  step  was  to  determine  very  accurately  the  position  of  vermilion 
with  respect  to  yellow.  There  are  many  separate  experiments  which 
influence  this  calculation  and  all  were  proportionately  w^eighted.  Then, 
using  vermilion  as  the  fixed  point  the  factors  (dot,  reduplicated, 
miniature,  and  sable)  which  lie  close  to  vermilion  were  plotted.  The 
same  process  was  repeated  in  locating  bar  with  respect  to  vermilion 
and  the  factors  about  bar  with  reference  to  bar.  The  last  step  was  to 
interpolate  the  factors  (club,  lethal  2,  lemon,  depressed,  and  shifted), 
which  form  a  group  about  midway  between  yellow  and  vermilion.  Of 
these,  club  is  the  only  one  whose  location  is  accurate.  The  apparent 
closeness  of  the  grouping  of  these  loci  is  not  to  be  taken  as  significant, 
for  they  have  been  placed  only  with  reference  to  the  distant  points 
yellow  and  vermihon  and  not  with  respect  to  each  other;  furthermore, 
the  data  available  in  the  cases  of  lemon  and  depressed  are  very  meager. 

The  factors  which  are  most  important  and  are  most  accurately 
located  are  yellow,  white  (eosin),  bifid,  club,  vermilion,  mmiature, 
sable,  forked,  and  bar.  Of  these  again,  white  (eosin),  vermilion,  and 
bar  are  of  prime  importance  and  will  probably  continue  to  claim  first 
rank.  Of  the  three  allelomorphs,  white,  eosin,  and  cherry,  eosin  is 
the  most  useful. 


24 


SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 


NOMENCLATURE. 

'Ihe  system  of  symbols  used  in  the  diagrams  and  table  headings  is 
as  follows:  The  factor  or  gen  for  a  recessive  mutant  character  is 
represented  by  a  lower-case  letter,  as  v  for  vermilion  and  m  for  mini- 
ature. I'he  symbolsforthedominant  mutant  characters  bar,  abnormal, 
and  notch  are  B',  A',  and  N'.  There  are  now  so  many  characters  that 
it  is  impossible  to  represent  all  of  them  by  a  single  letter.  We  there- 
fore add  a  subletter  in  such  cases,  as  bifid  (b;),  fused  (f  J,  and  lethal  2 
(I2).  In  the  case  of  multiple  allelomorphs  we  usually  use  as  the  base 
of  the  symbol  the  symbol  of  that  member  of  the  system  which  was  first 
found  and  add  a  letter  as  an  exponent  to  indicate  the  particular 
member,  as  y'  for  spot,  w''  for  eosin,  and  w"  for  cherry.  The  normal 
allelomorphs  of  the  mutant  gens  are  indicated  by  the  converse  letter, 
as  \'  for  not-vermilion,  B,  for  not-bifid,  and  b'  for  not-bar.  In  the 
table  headings  the  normal  allelomorphs  are  indicated  by  position  alone 

w*""                              B' 
without  the  use  of  a  symbol.     Thus  the  symbol 

indicates  that  the  female  in  question  carried  eosin,  not-vermilion,  and 
bar  in  one  chromosome  and  not-eosin,  vermilion,  and  not-bar  in  the 

other.     The  symbol  1 ttt  when  used  in  the  heading 

of  a  column  in  a  table  indicates  that  the  flies  classified  under  this 
heading  are  the  result  of  single  crossing-over  between  eosin  and  ver- 

.  .      w^                             B' 
milion  m  a  mother  which  was  of  the  composition ; 

the  symbol  tells  at  the  same  time  that  the  flies  that  result  from  a 
single  cross-over  between  eosin  and  vermilion  in  the  mother  are  of  the 
two  contrary  classes,  eosin  bar  and  vermilion.  When  a  fly  shows  two 
or  more  non-allelomorphic  characters  the  names  are  written  from  left 
to  right  in  the  order  of  their  positions  from  the  zero  end  of  the  map. 


PART  II.     NEW  DATA. 
WHITE. 

(Plate  II,  figure  ii.) 

The  recessive  character  white  eye-color,  which  appeared  in  May 
1910,  was  the  first  sex-linked  mutation  in  Drosophila  (Morgan,  1910^, 
1910^).  Soon  afterwards  (June  1910)  rudimentary  appeared,  and  the 
two  types  were  crossed  (Morgan,  1910c).  Under  the  conditions  of 
culture  the  viability  of  rudimentary  was  extremely  poor,  but  the  data 
demonstrated  the  occurrence  of  recombination  of  the  factors  in  the 
ovogenesis  so  that  white  and  rudimentary,  thougl^  both  sex-linked, 
were  brought  together  into  the  same  individual.  The  results  were  not 
fully  recognized  as  linkage,  because  white  and  rudimentary  are  so  far 
apart  in  the  chromosome  that  they  seemed  to  assort  freely  from  each 
other. 

Owing  to  the  excellent  viability  and  the  perfect  sharpness  of  sepa- 
ration, white  was  extensively  used  in  linkage  experiments,  especially 
with  miniature  and  yellow  (Morgan,  191 1^;  Morgan  and  Cattell,  191 2 
and  1913).  White  has  been  more  extensively  used  than  any  other 
character  in  Drosophila,  though  it  is  now  being  used  very  little  because 
of  the  fact  that  the  double  recessives  of  white  with  other  sex-linked 
eye-colors,  such  as  vermilion,  are  white,  and  consequently  a  separation 
into  the  true  genetic  classes  is  impossible.  The  place  of  white  has  been 
taken  by  eosin,  which  is  an  allelomorph  of  white  and  which  can  be 
readily  used  with  any  other  eye-color. 

The  locus  of  white  and  its  allelomorphs  is  only  l.i  units  from  that 
of  yellow,  which  is  the  zero  of  the  chromosome.  Yellow  and  white 
are  very  closely  linked,  therefore  giving  only  about  one  cross-over  per 
100  flies. 

All  the  pubHshed  data  upon  the  linkage  of  white  with  other  sex- 
linked  characters  have  been  collected  into  table  65. 

RUDIMENTARY. 

Rudimentary,  which  appeared  in  June  1910,  was  the  second  sex- 
Hnked  character  in  Drosophila  (Morgan,  i9ior).  Its  viability  has 
always  been  very  poor;  in  this  respect  it  is  one  of  the  very  poorest  ol 
the  sex-Hnked  characters.  The  early  linkage  data  (Morgan,  1911^) 
derived  from  mass  cultures  have  all  been  discarded.  By  breedmg  from 
a  single  Fi  female  in  each  large  culture  bottle  it  has  been  possible  to 
obtain  results  which  are  fairly  trustworthy  (Morgan,  191 2^:;  Morgan 
and  Tice,  1914).  These  data  appear  in  table  65,  which  summarizes 
all  the  published  data. 

35 


26 


SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 


The  locus  of  rudimentary  is  at  55.1,  for  a  longtime  the  extreme  right 
end  of  the  known  chromosome,  though  recently  several  mutants  have 
been  found  to  lie  somewhat  beyond  it. 


Fig.  a. — a,  nulimentary  wing;  b.  the  wild  fly  for  comparison. 

The  rudimentary  males  are  perfectly  fertile,  but  the  rudimentary 
females  rarely  produce  any  offspring  at  all,  and  then  only  a  very  few. 
The  reason  for  this  is  that  most  of  the  germ-cells  cease  their  develop- 
ment in  the  early  growth  stage  of  the  eggs  (Morgan,  1915a). 

MINIATURE. 

(Plate  II,  figures  7  and  8.) 

The  recessive  sex-linked  mutant  miniature  wings  appeared  in  August 
1910  (Morgan,  1911^  and  19x2^).  The  viability  of  miniature  is  fair, 
and  this  stock  has  been  used  in  linkage  experiments  more  than  any 


NEW    DATA. 


27 


re 


other,  with  the  single  exception  of  white.  While  the  win^s  of  miniatu 
usually  extend  backwards,  they  are  sometimes  held  out  at  right  angles 
to  the  body,  and  especially  in  acid  bottles  the  miniature  flies  easily 
become  stuck  to  the  food  or  the  wings  become  stringy,  so  that  other 
wing  characters  are  not  easy  to  distinguish  in  those  flies  which  are  also 
miniature.  At  present  vermilion,  whose  locus  is  at  33,  in  being  used 
more  frequently  in  linkage  work.  The  locus  of  miniature  at  36.1  is 
slightly  beyond  the  middle  of  the  chromosome. 

VERMILION. 

(Plate  II,  figure  lo.) 

The  recessive  sex-Hnked  mutant  vermilion  eye-color  (Morgan,  igiic 
and  1912^)  appeared  in  November  1910,  and  has  appeared  at  least 
twice  since  then  (Morgan  and  Plough,  1915).  This  is  one  of  the  best 
of  the  sex-linked  characters,  on  account  of  its  excellent  viability,  its 
sharp  distinction  from  normal  with  very  little  variability,  its  value  as 
a  double  recessive  in  combination  with  other  sex-linked  eye-colors, 
and  because  of  its  location  at  33.0,  very  near  to  the  middle  of  the  known 
chromosome. 

YELLOW. 

(Plate  I,  figure  5.) 

The  recessive  sex-linked  mutant  yellow  body  and  wing-color  ap- 
peared in  January  1911  (Morgan,  1911c  and  191213).  Its  first  appear- 
ance was  in  black  stock;  hence  the  fly  was  a  double  recessive,  then 
called  brown.  Later  the  same  mutation  has  appeared  independently 
from  gray  stock.  Yellow  was  found  to  be  at  the  end  of  the  X  chromo- 
some, and  this  end  was  arbitrarily  chosen  as  the  zero  or  the  "left  end," 
while  the  other  gens  are  spoken  of  as  lying  at  various  distances  to  the 
right  of  yellow.  Recently  a  lethal  gen  has  been  located  less  than  one- 
tenth  of  a  unit  (  —  0.04)  to  the  left  of  yellow,  but  yellow  is  still  retained 
as  the  zero-point. 

The  viability  of  yellow  is  fairly  good  and  the  character  can  be  sepa- 
rated from  gray  with  great  facility,  and  in  consequence  yellow  has  been 
used  extensively,  although  at  present  it  is  being  used  less  than  formerly, 
since  eosin  lies  only  i.i  units  distant  from  yellow  and  is  generally 
preferred. 

ABNORMAL  ABDOMEN. 

(Plate  I,  figure  4.) 

The  dominant  sex-linked  character  abnormal  abdomen  appeared  in 
July  191 1  (Morgan,  1911^).  It  was  soon  found  that  the  realization  ot 
the  abnormal  condition  depended  greatly  upon  the  nature  of  the  envi- 
ronment (Morgan,  1912).  Recently  a  very  extensive  study  of  this 
character  has  been  published  (Morgan,  191 5).  As  this  case  has  been 
reviewed  in  the  introduction,  there  is  little  further  to  be  said  here. 


28 


SEX-LINKED    INHERITANCE    IN   DROSOPHILA. 


Because  of  the  change  that  takes  place  as  the  culture  grows  older  (the  \ 
abnormal  changing  to  normal),  this  character  is  not  of  much  value  in 
linkage  work.  The  location  of  the  factor  in  the  X  chromosome  at  2.4 
has  been  made  out  from  the  data  given  by  Morgan  (191 5^).  These  data, 
which  in  general  include  only  the  abnormal  classes,  are  summarized 
in  table  i. 

Table  1, — Linkage  data,  from  Morgan,  1915b. 


Gens. 

Total. 

Cross- 
overs. 

Cross-over 
values. 

Yellow  white. . . 

28,018 

15,314 
16,300 

334 
299 
277 

1.2 
2.0 
1-7 

Yellow  abnormal 

White  abnormal 

EOSIN. 

(Plate  II,  figures  7  and  8.) 

The  recessive  sex-linked  mutation  eosin  eye-color  appeared  in 
August  1911  m  a  culture  of  white-eyed  flies  (Morgan  1912a)  The 
eye-color  is  different  in  the  male  and  female,  the  male  being  a  light 
pinkish  yellow,  while  the  female  is  a  rather  dark  vellowish  pink.  Eosin 
is  allelomorphic  to  white  and  the  white-eosin  compound  or  heterozygote 
has  the  color  of  the  eosin  male.  There  is  probablv  no  special  sig- 
nihcance  in  this  coincidence  of  color,  since  similar  dilutions  to  various 
degrees  have  been  demonstrated  for  all  the  other  eye-colors  tested 
(Morgan  and  Bridges,  1913).  Since  eosin  is  allelomorphic  to  white 
Its  locus  is  also  at  i.i.  Eosin  is  the  most  useful  character  among 
all  those  in  the  left  end  of  the  chromosome. 

BIFID. 

The  sex-hnked  wing  mutant  bifid,  which  appeared  in  November 
191 1,  IS  characterized  by  the  fusion  of  all  the  longitudinal  veins  into  a 
heavy  stalk  at  the  base  of  the  wing.  The  wing  stands  out  from  the 
body  at  a  wide  angle,  so  that  the  fusion  is  easily  seen.  At  the  tip 
ot  the  wing  the  third  longitudinal  vein  spreads  out  into  a  delta  which 
reaches  to  the  marginal  vein.  The  fourth  longitudinal  vein  reaches 
the  margin  only  rarely.  There  is  very  often  opposite  this  vein  a  great 
bay  in  the  margin,  or  the  whole  wing  is  irregularly  truncated 

1  he  stock  of  bifid  was  at  first  extremely  varied  in  the  amount  of  this 
truncation  By  selection  a  stock  was  secured  which  showed  only  verv 
greatly  reduced  wings  like  those  shown  in  figures  a,  b.  Another  stock 
(hgs.  f ,  d)  was  secured  by  outcrossing  and  selection  which  showed  wines 
ot  nearly  normal  size  and  shape,  which  always  had  the  bifid  stalk 
generally  the  spread  positions  (not  as  extreme),  and  often  the  delta  and 
the  shortened  fourth  longitudinal  vem.  We  believe  that  the  extreme 
reduction  in  size  seen  in  the  one  stock  was  due  to  an  added  modifier  of 


NEW    DATA. 


29 


the  nature  of  beaded,  since  this   could   be  eliminated   by  outcrossing 
and  selection. 


c      ^^-^TTTf-r-  ;■-'  ■~i.;\-ii-nrrF' 


Fig   B -Bifid  wing,    c  and  d  show  the  typical  condition  of  bifid  wings.    ^U  the  longitudinal  v^^^^^^ 
are  fused  into'a  heavy  stalk  at  the  base  of  the  wing,     a  shows  the  JVP'-^P-^-^-^^^^^^J^^J 
the  bifid  wings  are  held.     The  small  size  of  the  wings  in  a  and  h  1.  due  to  the  action  o. 
modifier  of  the  nature  of  "beaded"  which  has  been  eliminated  in  c,  d. 

LINKAGE    OF    BIFID  WITH  YELLOW,  WITH  WHITE,  AND  WITH  VERMILION. 

The  stock  of  the  normal  (not-beaded)  bifid  was  used  by  Dr.   R. 
Chambers,  Jr.,  for  determming  the  chromosome  locus  of  bihd  by  means 
of  its  linkage  relations  to  vermilion,  white,  and  yellow  (Chambers 
1913).     We  have  attempted  to  bring  together  in  table  2  the  complete 
data  and  to  calculate  the  locus  of  bifid. 

Table  2.— Linkage  data,  from  Chambers,  /p/j. 


Gens. 


Yellow  bifid .  . 
White  bifid  .  .  . 
Bifid  vermilion 


Total. 


3,175 

20,800 

2,509 


Cross- 
overs. 


182 

1,127 

806 


Cross-over 
values. 


S-8 

5-3 

32.1 


30 


SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 


I 


In  the  crosses  between  white  and  bifid  there  were  1,127  cross-overs 
in  a  total  of  20,800  available  individuals,  which  gives  a  cross-over  value 
of  5.  V  In  the  crosses  between  yellow  and  bifid  there  were  182  cross- 
overs in  a  total  of  3,175  available  individuals,  which  gives  a  cross-over 
value  of  5.8.  In  crosses  between  bifid  and  vermilion  there  were  806 
cross-overs  in  a  total  of  2,509,  which  gives  a  cross-over  value  of  32.1. 
On  the  basis  of  all  the  data  summarized  in  table  65,  bifid  is  located  at 
6.3  to  the  right  of  yellow. 

LINKAGE  OF  CHERRY,   BIFID,  AND  VERMILION. 

In  a  small  experiment  of  our  own,  three  factors  were  involved — 
cherry,  bifid,  and  vermilion.  A  cherry  vermilion  female  was  crossed 
to  a  bifid  male.  Two  daughters  were  back-crossed  singly  to  white 
bifid  males.  The  female  offspring  will  then  give  data  for  the  linkage  of 
cherry  white  with  bifid,  while  the  sons  will  show  the  linkage  of  the 
three  gens,  cherry,  bifid,  and  vermilion.  The  results  are  shown  in 
table  3. 


Table  3. — Pi  ch 

frry  vermilion  9  9    X  bifid   cTcf. 
zvhite  bifid  cf  cf . 

B.  C. 

^Fi« 

ild-ty-pe 

9   X 

Refer- 
ence. 

Fi  females. 

Fi  males. 

Non-cross- 
overs. 

Cross-overs. 

W^ 

bi 

V        w^  b 

w^ 

yv\  bi . V 

V 

bi'v 

White- 
cherry 

Bifid. 

White- 
cherry 
bifid. 

Wild- 
type. 

Cherry 

ver- 
milion. 

R-r  ,  1  Cherry 

^'^^i   bifid. 

1 

1 

Ver- 
milion. 

Cherry. 

Bifid 
ver- 
milion. 

vermilion.    ^" 

1 

262 
263 

Total. 

40 
47 

46 
45 

I 
3 

2 
3 

45 
30 

1 
38;      3 
50         I 

2 
3 

II 

8 

13 
10 

I 

87 

91 

4 

S 

75 

88         4            5 

19 

23 

I 

0 

*H.  C.  here  and  throughout  stands  for  back-cross. 


Both  males  and  females  give  a  cross-over  value  of  5  units  for  cherry 
bifid,  which  is  the  value  determined  b}'  Chambers.  The  order  of  the 
factors,  viz,  cherry,  bifid,  vermilion,  is  established  by  taking  advantage 
of  the  double  cross-over  classes  in  the  males.  The  male  classes  give 
a  cross-over  value  of  20  for  bifid  vermilion  and  24  for  cherry  vermilion, 
which  are  low  compared  with  values  given  by  other  experiments.  The 
locus  of  bifid  at  6.3  is  convenient  for  many  linkage  problems,  but  this 
advantage  is  largely  offset  by  the  liability  of  the  bifid  flies  to  become 
stuck  in  the  food  and  against  the  sides  of  the  bottle.  Bifid  flies  can  be 
separated  from  the  normal  with  certainty  and  with  great  ease. 


NEW   DATA. 


REDUPLICATED  LEGS. 


31 


In  November  191 2  Miss  Mildred  Hoge  found  that  a  certain  stock 
was  giving  some  males  whose  legs  were  reduplicated,  either  completely 
or  only  with  respect  to  the  terminal  segments  (described  and  figured, 
Hoge,  1915).  Subsequent  work  by  Miss  Hoge  showed  that  the  con- 
dition was  due  to  a  sex-linked  gen,  but  that  at  room  temperature  not 
all  the  flies  that  were  genetically  reduplicated  showed  reduplication. 
However,  if  the  flies  were  raised  through  the  pupa  stage  in  the  ice-box 
at  a  temperature  of  about  10°  to  12°  a  majority  of  the  flies  which  were 
expected  to  show  reduplication  did  so.  The  most  extremely  redupli- 
cated individual  showed  parts  of  14  legs. 

In  studying  the  cross-over  values  of  reduplicated,  only  those  flies 
that  have  abnormal  legs  are  to  be  used  in  calculation,  as  in  the  case 
of  abnormal  abdomen  where  the  phenotypically  normal  individuals 
are  partly  genetically  abnormal.  Table  4  gives  a  summary  of  the 
data  secured  by  Miss  Hoge. 

Table  4. — Summary  of  linkage  data  upon  reduplicated  legs,  from  Hoge,  iQij. 


Gens. 

Total. 

Cross- 
overs. 

Cross-over 
values. 

White  reduolicated 

418 
667 

S83 

121 
II 

120 

29.0 

1-7 
20.6 

Reduplicated  vermilion 

Reduolicated  bar 

The  most  accurate  data,  those  upon  the  value  for  reduplicated  and 
vermilion,  give  for  reduplicated  a  distance  of  1.7  from  vermilion,  either 
to  the  right  or  to  the  left.  The  distance  from  white  is  29,  which  would 
place  the  locus  for  reduplication  to  the  left  of  vermilion,  which  is  at  33. 
The  data  for  bar  give  a  distance  of  21,  but  since  bar  is  itself  24  units 
from  vermilion,  this  distance  of  21  would  seem  to  place  the  locus  to 
the  right  of  vermilion.  The  evidence  is  slightly  in  favor  of  this  position 
to  the  right  of  vermilion  at  34.7,  where  reduplicated  may  be  located 
provisionally.  In  any  case  the  locus  is  so  near  to  that  of  vermilion 
that  final  decision  must  come  from  data  involving  double  crossing-over, 
/.  f.,  from  a  three-locus  experiment. 


LETHAL  I. 

In  February  191 2  Miss  E.  Rawls  found  that  certain  females  from  a 
wild  stock  were  giving  only  about  half  as  many  sons  as  daughters. 
Tests  continuing  through  five  generations  showed  that  the  sons  that 
appeared  were  entirely  normal,  but  that  half  of  the  daughters  gave 
again  2  :  i  sex-ratios,  while  the  other  half  gave  normal  i  :  i  sex-ratios. 


3^ 


SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 


The  explanation  of  this  mode  of  transmission  became  clear  when  it 
was  found  that  the  cause  of  the  death  of  half  of  the  males  was  a 
particular  factor  that  had  as  definite  a  locus  in  the  X  chromosome  as 
have  other  sex-linked  factors  (Morgan,  191 2(?).  Morgan  mated  females 
(from  the  stock  sent  to  him  by  Miss  Rawls)  to  white-eyed  males. 
Half  of  the  females,  as  expected,  gave  2:1  sex-ratios,  and  daughters 
from  these  were  again  mated  to  white  males.  Here  once  more  half  of 
the  daughters  gave  2  :  i  sex-ratios,  but  in  such  cases  the  sons  were 
nearly  all  white-eyed  and  only  rarely  a  red-eyed  son  appeared,  when 
under  ordinary  circumstances  there  should  be  just  as  many  red  sons 
as  white  sons.  The  total  output  for  11  such  females  was  as  follows 
(Morgan,  1914Z?):  white?,  457;  red?,  433;  white  cf,  370;  redcf,  2. 
It  is  evident  from  these  data  that  there  must  be  present  in  the  sex-chro- 
mosome a  gen  that  causes  the  death  of  every  male  that  receives  this 
chromosome,  and  that  this  lethal  factor  lies  very  close  to  the  factor  for 
white  eyes.  The  linkage  of  this  lethal  (now  called  lethal  i)  to  various 
other  sex-linked  gens  was  determined  (Morgan  1914Z?),  and  is  summa- 
rized in  table  5.  On  the  basis  of  these  data  it  is  found  that  the  gen 
lethal  I  lies  0.4  unit  to  the  left  of  white,  or  at  0.7. 

Table  5. — Summary  of  linkage  dataupon  lethal  i ,  from  Morgayi,  1914b,  pp.  81-Q2. 


Gens. 

Total. 

Cross- 
overs. 

Cross-over 
values. 

Yellow  lethal  1 

Yellow  miniature 

Lethal  1  white 

Lethal  1  miniature 

White  miniature 

131 
131 
1,763 
814 
994 

I 

45 

7 

323 
397 

0.8 

34  4 

0.4 

39-7 
39-9 

LETHAL  la. 

In  the  second  generation  of  the  flies  bred  by  Miss  Rawls,  one  female 
gave  (March  191 2)  only  3  sons,  although  she  gave  312  daughters.  It 
was  not  known  for  some  time  (see  lethals  3  and  T,a)  what  was  the 
cause  of  this  extreme  rarity  of  sons.  It  is  now  apparent,  however, 
that  this  mother  carried  lethal  i  in  one  X  and  in  the  other  X  a  new 
lethal  which  had  arisen  by  mutation.  The  new  lethal  was  very  close 
to  lethal  I,  as  shown  by  the  rarity  of  the  surviving  sons,  which  are 
cross-overs  between  lethal  i  and  the  new  lethal  that  we  may  call  lethal 
\a.  I  here  is  another  class  of  cross-overs,  namely,  those  which  have 
lethal  I  and  get  lethal  \a  by  crossing-over.  These  doubly  lethal  males 
must  also  die,  but  since  they  are  theoretically  as  numerous  as  the  males 
(3)  free  from  both  lethals,  we  must  double  this  number  (3X2)  to  get 
the  total  number  of  cross-overs.  There  were  312  daughters,  but  as 
the  sons  are  normally  about  96  per  cent  of  the  number  of  the  females, 


NEW    DATA.  33 

we  may  take  300  as  the  number  of  the  males  which  died.  Tht-re 
must  have  been,  then,  about  2  percent  of  crossing-over,  which  makes 
lethal  la  lie  about  2  units  from  lethal  i.  This  location  of  lethal 
I  a  is  confirmed  by  a  test  that  Miss  Rawls  made  of  the  daughters  (jf 
the  high-ratio  female.  Out  of  98  of  these  daughters  none  repeated  the 
high  sex-ratio  and  only  2  gave  i  9  :  i  cf  ratios.  The  two  daughters 
which  gave  i :  i  ratios  are  cross-overs.  There  should  be  an  equal  number 
of  cross-overs  which  contain  both  lethals.  These  latter  would  not  be 
distinguishable  from  the  non-cross-over  females,  each  of  which  carries 
one  or  the  other  lethal.  In  calculation,  allowance  can  be  made  for  them 
by  doubling  the  number  of  observed  cross-overs  (2X2)  and  taking 
98  —  2    as   the   number  of  non-cross-overs.     The  cross-over  fraction 

^  gives  2.6  as  the  distance  between  the  two  lethals.     Lethal 

300-f96 

I  a  is  probably  to  the  right  of  lethal  i  at  0.7-1-2.6  =  3.3. 

SPOT. 

(Plate  II,  figures  14  to  17.) 

In  April  191 2  there  was  found  in  the  stock  of  yellow  flies  a  male 
that  differed  from  yellow  in  that  it  had  a  conspicuous  light  spot  on  the 
upper  surface  of  the  abdomen  (Morgan,  1914^).  In  yellow  flies  this 
region  is  dark  brown  in  color.  In  crosses  with  wild  flies  the  spot 
remained  with  the  yellow,  and  although  some  30,000  flies  were  raised, 
none  of  the  gray  offspring  showed  the  spot,  which  should  have  occurred 
had  crossing-over  taken  place.  The  most  probable  interpretation  of 
spot  is  that  it  was  due  to  another  mutation  in  the  yellow  factor,  the 
first  mutation  being  from  gray  to  yellow  and  the  second  from  yellow 
to  spot. 

Spot  behaves  as  an  allelomorph  to  yellow  in  all  crosses  where  the  two 
are  involved  and  is  completely  recessive  to  yellow,  2.  e.,  the  yellow-spot 
hybrid  is  exactly  like  yellow.  A  yellow-spot  female,  back-crossed  to  a 
spot  male,  produces  yellows  and  spots  in  equal  numbers. 

In  a  cross  of  spot  to  black  it  was  found  that  the  double  recessive,  spot 
black,  flies  that  appear  in  F2  have,  in  addition  to  the  spot  on  the  abdo- 
men, another  spot  on  the  scutellum  and  a  light  streak  on  the  thorax. 
These  two  latter  characters  ("dot  and  dash  ")  are  very  sharply  marked 
and  conspicuous  when  the  flies  are  young,  but  they  are  only  juvenile 
characters  and  disappear  as  the  flies  become  older.  1  he  spot  flies 
never  show  the  "dot  and  dash"  clearly,  and  it  only  comes  out  when 
black  acts  as  a  developer.  These  characters  furnish  a  good  illustration 
of  the  fact  that  mutant  gens  ordinarily  affect  many  parts  of  the  body, 
though  these  secondary  effects  often  pass  unnoticed. 

In  the  F2  of  the  cross  of  spot  by  black  one  yellow  black  fly  appeared, 
although  none  are  expected,  on  the  assumption  that  spot  and  yellow 


34  SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 

are  allelomorphic.  Unless  due  to  crossing-over  it  must  have  been  a 
mutation  from  spot  back  to  yellow.  Improbable  as  this  may  seem  to 
those  who  look  upon  mutations  as  due  to  losses  from  the  germ-plasm, 
yet  we  have  records  of  several  other  cases  where  similar  mutations 
"backwards"  have  taken  place,  notably  in  the  case  of  eosin  to  white, 
under  conditions  where  the  alternative  interpretation  of  crossing-over 
is  excluded. 

SABLE. 

(Plate  I,  figure  2.) 

In  an  experiment  involving  black  body-color^  a  fly  appeared  (July 
19,  191 2)  whose  body-color  difi^ered  slightly  from  ordinary  black  in 
that  the  trident  mark  on  the  thorax  was  sharper  and  the  color  itself 
was  brighter  and  clearer.  This  fly,  a  male,  was  mated  to  black  females 
and  gave  some  black  males  and  females,  but  also  some  gray  (wild 
body-color)  males  and  females,  showing  not  only  that  he  was  heterozy- 
gous for  ordinary  recessive  black,  but  at  the  same  time  that  his  dark 
color  must  be  due  to  another  kind  of  black.  The  gray  Fi  flies  when 
mated  together  gave  a  series  of  gray  and  dark  flies  in  F2  about  as  follows: 
In  the  females  3  grays  to  i  dark;  in  the  males  3  grays  to  5  dark  in  color. 
The  result  indicated  that  the  new  black  color,  which  we  call  sable,  was 
due  to  a  sex-linked  factor.  It  was  difficult  to  discover  which  of  the 
heterogeneous  Fj  males  were  the  new  blacks.  Suspected  males  were 
bred  (singly)  to  wild  females,  and  the  F2  dark  males, from  those  cultures 
that  gave  the  closest  approach  to  a  2  gray  9  :  i  graycf  :  i  darkcf ,  were 
bred  to  their  sisters  in  pairs  in  order  to  obtain  sable  females  and  males. 
I  hus  stock  homozygous  for  sable  but  still  containing  black  as  an 
impurity  was  obtained.  It  became  necessary  to  free  it  from  black  by 
successive  individual  out-crossings  to  wild  flies  and  extractions. 

This  account  of  how  sable  was  purified  shows  how  difficult  it  is  to 
separate  two  recessive  factors  that  give  closely  similar  somatic  eff'ects. 
If  a  character  like  sable  should  be  present  in  any  other  black  stock,  or 
if  a  character  like  black  should  be  present  in  sable,  very  erratic  results 
would  be  obtained  if  such  stocks  were  used  in  experiments,  before  such 
a  population  had  been  separated  into  its  component  races. 

Sable  males  of  the  purified  stock  were  mated  to  wild  females  and  gave 
wild-type  (gray)  males  and  females.  These  inbred  gave  the  results 
shown  in  table  6. 

No  sable  females  appeared  in  Fo,  as  seen  in  table  6.  The  reciprocal 
cross  gave  the  results  shown  in  table  7. 

'The  first  dark  body-color  mutation  "black"  (see  plate  II,  figs.  7,  8)  had  appeared  much  earlier 
(.Morgan  igiib,  1912c;.  It  is  an  autosomal  character,  a  member  of  the  second  group  of  linked 
gens.  Still  another  dark  mutant,  "ebony,"  had  also  appeared,  which  was  found  to  be  a  member 
of  the  third  group  of  gens. 


NEW    DATA. 


35 


The  Fi  males  were  sable  like  their  mother.  The  evidence  thus  shows 
that  sable  is  a  sex-linked  recessive  character.  Our  next  step  was  to 
determine  the  linkage  relations  of  sable  to  certain  other  sex-linked 
gens,  namely,  yellow,  eosin,  cherry,  vermilion,  miniature,  and  bar. 


Table  6.— Pi  wild  9  9  X  sable  cT.     fi  zvild-type  9  9  X  Fi  zcild-ty 


■type  cfcf. 


Reference.* 

Wild-type  9  • 

Wild-type  cf . 

Sable  cf . 

88  C 

143  C 

146  C 

Total .  . . 

218 

24s 
200 

100 
108 
"5 

70 

72 
82 

663 

323 

224 

'  Wherever  reference  numbers  are  given,  these  denote  the 
pages  in  the  note-books  of  Bridges  upon  which  the  original 
entries  for  each  culture  are  to  be  found. 

Table  7. — Pi  sable  9  X  wild  cTcf .     Fi  wild-type  9  X  A  sable  cT. 


Reference. 

Wild-type  9  . 

Wild-type  cf  ■ 

Sable  9 . 

Sable  cf. 

4I 

10 

10 

6 

10 

LINKAGE  OF  YELLOW  AND  SABLE. 

The  factor  for  yellow  body-color  lies  at  one  end  of  the  known  series 
of  sex-linked  gens.  As  already  stated,  we  speak  of  this  end  as  the  left 
end  of  the  diagram,  and  yellow  as  the  zero  in  locating  factors. 

When  yellow  (not-sable)  females  were  mated  to  (not-yellow)  sable 
males  they  gave  wild-type  (gray)  daughters  and  yellow  sons.  These 
inbred  gave  in  F2  two  classes  of  females,  namely,  yellow  and  gray,  and 
four  classes  of  males,  namely,  yellow  and  sable  (non-cross-overs),  wild 
type,  and  the  double  recessive  yellow  sable  (cross-overs).  From  off- 
spring (F3)  of  the  F2  yellow  sable  males  by  F2  yellow  females,  pure  stock 
of  the  double  recessive  yellow  sable  was  made  up  and  used  in  the 
crosses  to  test  linkage. 

In  color  the  yel!ow  sable  is  quite  similar  to  yellow  black,  that  is,  a 
rich  brown  with  a  very  dark  brown  trident  pattern  on  the  thorax. 
Yellow  sable  is  easier  to  distinguish  from  yellow  than  is  yellow  black, 
even  when  the  flies  have  not  yet  acquired  their  adult  body-color. 

Yellow  sable  males  were  bred  to  wild  females  and  Fi  consisted  of 
wild-type  males  and  females.  These  inbred  gave  the  results  shown  m 
table  8. 


36  SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 

Table  8.— Pi  a-ild  9  9  X  yellow  sable  cTcf  •     fi  wild-type  9  9  X 

F\  wild-type  cf  cT . 


Reference. 

Wild- 
type  9 . 

Non-cross-over  cf. 

Cross-over  cf  • 

Total 
males. 

Cross-over 
value. 

Yellow  sable. 

Wild-type. 

Yellow. 

Sable. 

44  I 

202 

384 

no 
104 

43 

58 

75 
71 

36 
60 

264 
293 

42 
45 

45  I       

Total 

676 

214 

lOI 

146 

96 

557 

43 

Some  of  the  Fi  females  were  back-crossed  to  yellow  sable  males  and 
gave  the  data  for  table  9. 

Table  9.— Pi  wild-type  9  9  X  yellow  sable  d'd'.     B.C.Fi  wild-type  9  X 

yellow  sable  cf  cf . 


Reference. 

Non-cross-overs. 

Cross-overs. 

Total. 

Cross-over 
value. 

Wild-type. 

Yellow  sable. 

Yellow. 

Sable. 

31I 

49  I 

Total .  . 

108 
265 

SI 

175 

58 
161 

56 
169 

273 
770 

42 

43 

373 

226 

219 

225 

1.043 

43 

In  these  tables  the  last  column  (to  the  right)  shows  for  each  culture 
the  amount  of  crossing-over  between  yellow  and  sable.  These  values 
are  found  by  dividing  the  number  of  cross-overs  by  the  total  number  of 
individuals  which  might  show  crossing-over,  that  is,  males  only  or  both 
males  and  females,  as  the  case  may  be.  Free  assortment  would  give 
50  per  cent  of  cros.s-overs  and  absolute  linkage  o  per  cent  of  cross-overs. 
Except  where  the  percentage  of  crossing-over  is  very  small  these  values 
are  expressed  to  the  nearest  unit,  since  the  experimental  error  might 
make  a  closer  calculation  misleading. 

The  combined  data  of  tables  8  and  9  give  686  cross-overs  in  a  total  of 
T,6oo  individuals  in  which  crossing-over  might  occur.  The  females  of 
table  8  are  all  of  one  class  (wild  type)  and  are  useless  for  this  calculation 
except  as  a  check  upon  viability.  The  cross-over  value  of  43  per  cent 
shows  that  crossing-over  is  very  free.  We  interpret  this  to  mean  that 
sable  is  far  from  yellow  in  the  chromosome.  Since  yellow  is  at  one  end 
of  the  known  series,  sable  would  then  occupy  a  locus  somewhere  near 
the  opposite  end.  This  can  be  checked  up  by  finding  its  linkage  rela- 
tions to  the  other  sex-linked  factors. 


NEW    DATA. 


LINKAGE    OF    CHERRY   AND    SABLE. 


37 


The  origin  of  cherry  eye-color  (Plate  II,  fig.  9)  has  been  given  by 
Safir  (Biol.  Bull.,  191 3).  From  considerations  which  will  be  dis- 
cussed later  in  this  paper  we  regard  cherry  as  allelomorphic  to  white  in 
a  quadruple  allelomorph  system  composed  of  white,  eosin,  cherry,  and 
their  normal  red  allelomorph.  Cherry  will  then  occupy  the  same  locus 
as  white,  which  is  one  unit  to  the  right  of  yellow,  and  will  show  the 
same  linkage  relations  to  other  factors  as  does  white.  A  slightly  lower 
cross-over  value  should  be  given  by  cherry  and  sable  than  was  given 
by  yellow  and  sable. 

When  cherry  (gray)  females  were  crossed  to  (red)  sable  males  the 
daughters  were  wild  type  and  the  sons  cherry.  Inbred  these  gave  the 
results  shown  in  table  10, 

Table  10. — Pi  cherry  9  9  X  sahle  cf  cf.     Fi  wild-type  9  X  Pi  cherry  d'cf . 


Reference. 

Wild- 
type  9. 

Cherry 

9. 

Non-cross-over  cT. 

Cross-over  cT. 

Total 
males. 

Cross- 
over 
value. 

Cherry. 

Sable. 

Cherry  sable. 

Wild-type. 

24  I 

55  I 

S5'I 

Total .  .  . 

94 

lOI 

96 

105 

131 

94 

51 

63 

52 

42 

52 

31 

20 
38 
29 

43 
48 
30 

156 
201 
142 

40 

43 
42 

291 

330 

166 

125 

87 

121 

499 

42 

The  percentage  of  crossing-over  between  cherry  and  sable  is  42. 
Since  cherry  is  one  point  from  yellowy  this  result  agrees  extremely  well 
with  the  value  43  for  yellow  and  sable.  Since  yellow  and  eosin  lie  at 
the  left  end  of  the  first  chromosome,  the  high  values,  namely,  43  and  42, 
agree  in  making  it  very  probable  that  sable  lies  near  the  other  end 
(z.  e.y  to  the  right).  Sable  will  he  farther  to  the  right  than  vermilion, 
for  vermilion  has  been  shown  elsewhere  to  give  33  per  cent  of  crossing- 
over  with  eosin.  The  location  of  sable  to  the  right  of  vermilion  has  in 
fact  been  substantiated  by  all  later  work. 


LINKAGE  OF  EOSIN,  VERMILION,  AND  SABLE. 

Three  loci  are  involved  in  the  next  experiment.  Since  eosin  is  an 
allelomorph  of  cherry,  it  should  be  expected  to  give  with  sable  the 
same  cross-over  value  as  did  cherry.  When  eosin  (red)  sable  females 
were  crossed  to  (red)  vermiHon  (gray)  males,  the  daughters  were  wild 
type  and  the  males  were  eosin  sable.  Inbred  these  gave  the  classes 
shown  in  table  11. 


38 


SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 


Table  11. — Pi  eosin  sable  9  X  vermilion  cf  cf .     Fi  wild-type  9  9  X  Fi  eosin 

sable  d'd^. 


Reference. 

Fj  females. 

Fi  males. 

W^        S 

W<^ 

we      s 

w" 

V 

s 

V   s 

W*  V    s 

s 

V 

Eosin 
sable. 

Wild-  r-^  •„ 
Losm. 
type. 

Sable. 

Eosin 
sable. 

Ver- 
milion. 

Eosin 
ver- 
milion. 

Sable. 

Eosin. 

Ver- 
milion 
sable. 

Eosin 
ver- 
milion 
sable. 

Wild- 
type. 

26  I ... . 
26'!.... 

Total . 

I3i 
96 

171        113 
146         86 

109 
78 

127 
74 

163 
128 

75 
76 

76 
59 

37 
18 

14 

21 

2 
4 

5 

3 

228 

317 

199 

187 

201 

291 

151 

135 

55 

35 

6 

8 

If  we  consider  the  male  classes  of  table  11,  we  find  that  the  smallest 
classes  are  eosin  vermilion  sable  and  wild  type,  which  are  the  expected 
double  cross-over  classes  if  sable  lies  to  the  right  of  vermilion,  as  indi- 
cated by  the  crosses  with  eosin  and  with  yellow.  The  classes  which 
represent  single  crossing-over  between  eosin  and  vermilion  are  eosin 
vermilion,  and  sable,  and  those  which  represent  single  crossing-over 
between  vermilion  and  sable  are  eosin  and  vermilion  sable.  These 
relations  are  seen  in  diagram  II. 

\v  V'  s 


^ 


X 


Diagram  II. — The  upper  line  represents  an  X  chromosome,  the  lower  Hne  its  mate. 
The  cross  connecting  lines  indicate  crossing-over  between  pairs  of  factors. 


Non-cross-overs 
Single  cross-overs 


Double  cross-overs 


w* 


w' 


w 


w* 


s  /Eosin  sable. 

V  \Vermilion. 

2^ fEosin  vermilion. 

s  {Sable. 


/.E 


osin. 


v      s      [Vermilion  sable. 

_^[ i_s     JEosIn  vermilion  sable. 

^     \Wild-type. 


If  we  consider  the  female  classes  of  table  11,  we  get  information  as  to 
the  cross-over  value  of  eosin  and  sable,  namely,  42  units.  The  male 
classes  will  be  considered  in  connection  with  the  cross  that  follows. 

The  next  experiment  involves  the  same  three  gens  which  now  enter 
in  different  relations.    A  double  recessive,  eosin  vermiHon  (gray)  female 


NEW    DATA. 


39 


was  mated  to  (red  red)  sable  males  and  gave  202  wild-type^  females 
and  184  eosin  vermilion  males.  Two  Fi  pairs  gave  the  results  shown 
in  table  12  (the  four  classes  of  females  not  being  separated). 

Table  12. — Pi  eosin  vermilion  9  9  X  sable  cf  cf .     Fi  wild-type  9  X  Fi 

eosin  vermilion  cf  cT . 


Reference. 

females. 

Fj  males. 

W«    V 

s 

W^        s 
V 

W^  v.s 

V   S 

Eosin 
ver- 
milion 

cT. 

Sable 

Eosin 
sable 

cf. 

Ver- 
milion 

d'. 

Eosin 

vermilion 

sable 

d. 

Wild- 
type 

d. 

Eosin 

Ver- 
milion 
sable 

59  C... 

61  c... 

Total.. 

133 

lOI 

40 

34 

33 
26 

7 
8 

16 
II 

5 

3 

5 
7 

2 

I 

I 

0 

234 

74 

59 

15 

27 

8 

12 

3 

I 

If  we  combine  the  data  for  males  given  in  table  12  with  those  of 
table  II,  we  get  the  following  cross-over  values.  Eosin  vermilion,  32; 
vermilion  sable,  12;  eosin  sable,  41. 

^In  addition  to  these  expected  Fi  wild-type  females  there  occurred  13  females  of  an  eye-color 
like  that  of  the  mutant  pink.  So  far  as  was  seen  none  of  the  Fj  males  differed  in  eye-color  from 
the  expected  eosin  vermilion.  Since  the  eosin  vermilion  and  sable  stocks  were  unrelated  and 
neither  was  known  to  contain  a  "pink"  as  an  impurity,  these  "pinks"  must  be  due  to  mutation 
of  an  unusual  kind.  That  these  " pinks"  were  really  products  of  the  cross  is  proven  by  the  result 
of  crossing  one  of  them  to  one  of  her  eosin  vermilion  brothers,  for  she  showed  herself  to  be  heterozy- 
gous for  eosin,  vermilion,  and  sable. 

Fi  "pink"  {Ref.  5/  C)   9   X  Fi  eosin  vermilion  d. 


Reference. 

Wild-type. 

Eosin  vermilion. 

Eosin. 

\'ermilion. 

9 

d 

9 

d 

9 

c^ 

9 

cP 

59  C 

59 

38 

43 

40 

15 

9 

x6 

17 

In  addition  to  the  combinations  of  eosin  and  vermilion,  sable  also  appeared  in  its  proper  dis- 
tribution, though  no  counts  were  made.  The  four  smaller  classes  are  cross-overs  between  eosin 
and  vermilion.  Since  no  "pinks"  appeared  the  color  is  recessive,  and  the  brother  was  not  hetero- 
zygous for  it. 

Two  other  "pink"  females  mated  to  wild  males  gave  similar  results  in  their  sons. 


Fi  "pink"  9 

X  tvild  d. 

Reference. 

Wild-type  9- 

Wild-type  d. 

Eosin  vermilion  cf . 

Eosin  d. 

Vermilion  c?". 

61  C 

lOI 

33 

37 

9 

II 

These  Fi  flies  should  all  be  heterozygous  for  "pink."  A  pair  of  wild-type  Hies  which  were 
mated  gave  a  3  :  1  ratio— wild  type  51  to  "  pink"  18.  From  the  "  pinks'  which  appeared  m  thi« 
cross  a  stock  was  made  which  was  lost  through  sterility.  Females  tested  to  males  of  true  pmk 
were  also  sterile,  so  that  no  solution  can  be  given  of  the  case. 


40 


SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 


LINKAGE  OF  MINIATURE  AND  SABLE. 

The  miniature  wing  has  been  described  (Morgan,  Science,  1911) 
and  the  wing  figured  (Morgan,  Jour.  Exp.  Zool.,  1911).  The  gen  for 
miniature  Hes  about  3  units  to  the  right  of  vermihon,  so  that  it  is  still 
closer  to  sable  than  is  vermilion.  The  double  recessive,  miniature 
sable,  was  made  up,  and  males  of  this  stock  were  bred  to  wild  females 
(long  gray).  The  wild-type  daughters  were  back-crossed  to  double 
recessive  males  and  gave  the  results  (mass  cultures)  shown  in  table  13. 

Table  13.— Pi  u-ild  9  9   X  miniature  sable  d'd'.     B.  C.  Fi  wild-type  9  9   X 

miniature  sable  cf  cf  • 


Reference. 

Non-cross-overs. 

Cross-overs. 

Total. 

Cross- 
over 
value. 

Miniature  sable. 

Wild-type. 

Miniature. 

Sable. 

38I 

43I 

46I 

Total .  . 

245 
191 

232 

283 
236 
274 

IS 
13 

24 

17 
18 
21 

560 
458 

SSI 

6 

7 
8 

668 

793 

52 

56 

i,S69 

7 

Since  the  results  for  the  male  and  the  female  classes  are  expected  to 
be  the  same,  the  sexes  were  not  separated.  The  combined  data  give 
7  per  cent  of  crossing-over  between  miniature  and  sable. 


LINKAGE  OF  VERMILION,  SABLE,  AND  BAR. 

Bar  eye  has  been  described  by  Mrs.  S.  C.  Tice  (1914).  It  is  a  domi- 
nant sex-linked  character,  whose  locus,  lying  beyond  vermilion  and 
sable,  is  near  the  right  end  of  the  chromosome  series,  that  is,  at  the 
end  opposite  yellow. 

In  the  first  cross  of  a  balanced  series  of  experiments  for  the  gens 
vermilion,  sable,  and  bar,  vermilion  (gray  not-bar)  entered  from  one 
side  (  9  )  and  (red)  sable  bar  from  the  other  ic^).  The  daughters  were 
bar  and  the  sons  vermilion.  The  daughters  were  back-crossed  singly 
to  the  triple  recessive  males  vermilion  sable  (not-bar),  and  gave  the 
data  included  in  table  14. 

In  the  second  cross,  vermilion  sable  (not-bar)  went  in  from  one  side 
(  9 )  and  (red,  gray)  bar  from  the  other.  The  daughters  were  bar  and 
the  sons  were  vermilion  sable.  Since  these  sons  have  the  three  reces- 
sive factors,  inbreeding  of  Fi  is  equivalent  to  a  triple  back-cross.  The 
results  are  given  by  pairs  in  table  15. 


NEW    DATA. 


41 


Table  14. — Pi  vermilion  9  9  X  sable  bar  cf  cf .     B.  C.  Fi  bar  9  X  vermilion 

sable  cTcf. 


Reference. 

V 

s    B' 

VjS  B' 

V    |B' 

s 

'    'B' 

Total. 

Cross-over  values. 

Ver- 
milion. 

Sable 
bar. 

Ver- 
milion 
sable 
bar. 

Wild- 
type. 

Ver- 
milion 
bar. 

Sable. 

Ver- 
milion 
sable. 

Bar. 

Ver- 
milion 
sable. 

Sable 
bar. 

Ver- 
milion 
bar. 

147  I.... 

148  I.... 

149  I.... 

150  I 

isii.... 

89 

90 

91 

Total . 

81 

103 

97 

95 

116 

89 

49 

104 

66 

108 
88 

75 
96 

94 

SO 
88 

12 

4 
10 
10 
II 
10 

4 
13 

15 
19 

8 
II 
IS 
19 

8 

IS 

IS 
II 

17 
21 

23 
IS 
IS 
12 

18 
II 

17 
22 
26 
II 

14 

12 

I 
I 

I 

I 
I 
2 

207 
256 
239 
236 
289 
239 
140 
244 

13 

9 

8 

10 

to 

13 

9 

II 

16 
9 
IS 
19 
18 
II 
21 
10 

29 
18 
22 

27 
26 
23 
29 
21 

734 

66s 

74 

no 

129 

131 

3 

4      1.850 

10 

14 

24 

Table  15. — Pi  vermilion  sable  9  9  X  bar  c^<f.     B.  C.  Fi  bar  9  X  vermilion 

sable  cf  c?'. 


V    s 

B' 

S 

B' 

V    S 

hM: 

Vf 

Total. 

Cross 

-over  values. 

Reference. 

Ver- 

Ver- 

Ver- 
milion 

WilH- 

Ver- 

Sable 

Ver- 

Sable 

Ver- 

milion 

Har 

milion 

Sable. 

sable 
bar. 

bar. 

milion 

bar. 

milion 

sable. 

bar. 

type. 

milion. 

sable. 

bar. 

105  I... . 

41 

75 

10 

4 

5 

II 

146 

10 

II 

21 

106  I.... 

59 

122 

16 

13 

II 

17 

238 

12 

12 

24 

107  I. ... 

92 

98 

8 

12 

16 

10 

236 

9 

II 

20 

116I.... 

III 

149 

19 

16 

20 

19 

I 

335 

II 

12 

22 

117I.... 

92 

117 

16 

14 

IS 

18 

272 

II 

12 

23 

126  I.... 

96 

160 

13 

13 

17 

35 

334 

8 

15 

23 

127I.... 
Total . 

117 

124 

13 

25 

24 

30 

I 

334 

i; 

16 

28 

608 

84s 

95 

97 

108 

140 

I 

I 

1.895 

10 

13 

23 

42 


SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 


In  the  third  cross,  vermiHon  (gray)  bar  entered  from  one  side  (  9  ) 
and  (red)  sable  (not-bar)  from  the  other  (cT).  The  daughters  are 
bar  and  the  sons  vermiHon  bar.  The  daughters  were  back-crossed 
singly  to  vermilion  sable  males  and  gave  the  data  in  table  i6. 


Table  16. — Pi  vermilion  bar  9  9  X  sable  cf  cf. 

sable  cTcf, 


B.  C.  Fi  bar  $  X  vermilion 


V 

B' 

V    S 

V 

V   s 

B' 

Reference. 

s 

B' 

s 

B' 

Total. 

Cross 

-over  values. 

Ver- 
milion 

Sable. 

!  Ver- 
milion 

Bar. 

Ver- 

Sable 
bar. 

Ver- 

milion 

sable 

bar. 

Wild- 

Ver- 
milion 

Sable 

Ver- 
milion 

bar. 

sable. 

mihon. 

type. 

sable. 

bar. 

bar. 

129  I.... 

132 

147 

IS 

IS 

19 

21 

I 

351 

9 

12 

20 

130I 

194 

168 

21 

17 

28 

2S 

454 

9 

12 

20 

131  I 

121 

89 

10 

20 

26 

II 

I 

279 

12 

14 

24 

137  I.. •• 

139 

"3 

19 

12 

33 

14 

331 

10 

IS 

24 

138I.... 

131 

128 

II 

II 

28 

24 

I 

334 

7 

16 

22 

139I.... 
Total. 

«3 

79 

4 

12 

17 

12 

207 

8 

14 

22 

800 

724 

80 

87 

151 

107 

3 

4 

1,956 

9 

14 

22 

In  the  fourth  cross,  vermilion  sable  bar  entered  from  one  side,  and 
(red  gray  not-bar)  wild  type  from  the  other.  The  daughters  were  bar 
and  the  sons  vermilion  sable  bar.  The  daughters  were  back-crossed 
singly  to  vermilion  sable  males,  with  the  results  shown  in  table  17. 


T.\BLE 

17.— 

Pi  vermilion  sable  bar 

9  9  X  tvild  cf  cT 

'.     B. 

C.F, 

bar  9  X 

vermilion 

sable  cf  cf  • 

V  s  B' 

V. 

V    S 

V.    .B' 

j 

Reference. 

's  B' 

*^ 

-+-H 

s 

Total. 

Cross 

-over  values. 

Ver- 
milion 
sable 
bar. 

Wild- 
type. 

Ver- 
milion. 

Sable 
bar. 

Ver- 
milion 
sable. 

Bar. 

Ver- 
milion 
bar. 

Sable. 

Ver- 
milion 
sable. 

Sable 
bar. 

Ver- 
milion 
bar. 

132I.... 

95 

108 

10 

13 

24 

22 

1 

272 

9 

17 

25 

133  I... 

112 

ISO 

18 

16 

26 

16 

I 

2 

341 

II 

13 

22 

134I.... 

84       95 

14 

7 

15 

16 

I 

232 

10 

14 

22 

I3SI... 

100 

86 

16 

17 

19 

22 

I 

261 

13 

16 

28 

152I..,. 

73 

88 

12 

8 

14 

18 

213 

9 

15 

24 

,, 

153!  ••• 

114 

I3« 

12 

12 

17 

17 

310 

8 

II 

19 

154!     • 
Total . 

63 

90 

10 

8 

8 

15 

194 

9 

12 

21 

■' 

641     755 

92 

81 

123 

126 

I 

4 

1,823 

10 

14 

23 

NEW    DATA. 


43 


In  tables  14  to  17  the  calculations  for  the  three  cross-over  values  for 
vermilion,  sable,  and  bar  are  given  for  the  separate  cultures  and  for  the 
totals.     The  latter  are  here  repeated. 


From — 

Vermilion 

Sable 

Vermilion 

sable. 

bar. 

bar. 

Table  14.  .  .  . 

10 

14 

24 

15  •••• 

10 

13 

23 

16.... 

9 

14 

22 

17.... 

10 

14 

23 

The  results  of  the  different  experiments  are  remarkably  uniform. 
There  can  be  no  doubt  that  the  cross-over  value  is  independent  of  the 
way  in  which  the  experiment  is  made,  whether  any  two  recessives  enter 
from  the  same  or  from  opposite  sides. 

Table  18. — Linkage  of  vermilion,  sable,  and  bar  with  balanced  viability. 


Total. 

■' 

Wild-type 

Vermilion 

755 
734 
724 
845 
608 
800 
66s 
641 

110 
92 
97 
87 
80 

95 
81 

74 

140 

151 
131 
126 
123 
129 
107 
108 

4 

I 

4 
4 

3 

I 
I 
3 

Sable 

Bar 

Vermilion  sable 

Vermilion  bar 

Sable  bar 

Vermilion  sable  bar.  .  .  . 
Total 

5,772 
76.7 

716 
9-53 

1,015 
13-49 

21 

0.28 

7,524 

Percentage 

In  table  18  the  data  from  each  of  the  four  separate  experiments  have 
been  combined  in  the  manner  explained,  so  that  viability  is  canceled 
to  the  greatest  extent.  The  amount  of  each  kind  of  cross-over  appears 
at  the  bottom  of  the  table.  The  total  amount  of  crossing-over  between 
vermilion  and  sable  is  the  sum  of  the  single  (9.53)  and  of  the  double 
(0.28)  cross-overs,  which  value  is  9.8.  Likewise  the  cross-over  value 
for  sable  bar  is  13.49+0.28  (  =  14),  and  for  vermilion  bar  is  9.53  +  13-49 
(  =  23).  By  means  of  these  cross-over  values  we  may  calculate  the 
coincidence  involved,  which  is  in  this  case 

0.0028X100  o 

; =  20  .  O 

0.0953+0.0028x0. 1349+0.0028 
This  value  shows  that  there  actually  occurs  only  about  21  per  cent 
of  the  double  cross-overs  which  from  the  values  of  the  single  cross-overs 
are  expected  to  occur  in  this  section  of  the  chromosome.  I  his  is  the 
result  which  is  to  be  anticipated  upon  the  chromosome  view,  for  if 
crossing-over  is  connected  with  loops  of  the  chromosomes,  and  if  these 
loops  have  an  average  length,  then  if  the  chromosomes  cross  over  at  one 


44 


SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 


point  it  is  unlikely  they  will  cross  over  again  at  another  point  nearer 
than  the  average  length  of  the  loop. 

The  calculation  of  the  locus  for  sable  gives  43.0. 

DOT. 

In  the  Fo,  from  a  cross  of  a  double  recessive  (white  vermilion)  female 
by  a  triple  recessive  (eosin  vermilion  pink)  male,  there  appeared,  July 
21,  191 2,  three  white-eyed  females  which  had  two  small,  symmetrically 
placed,  black,  granular  masses  upon  the  thorax.  These  "dots" 
appeared  to  be  dried  exudations  from  pores.  It  did  not  seem  possible 
that  such  an  effect  could  be  inherited,  but  as  this  condition  had  never 
been  observed  before,  it  seemed  worth  while  to  mate  the  three  females 
to  their  brothers.  In  the  next  generation  about  i  per  cent  of  the  males 
were  dotted.  From  these  females  and  males  a  stock  was  made  up 
which  in  subsequent  generations  showed  from  10  to  50  per  cent  of 
dot.  Selection  seemed  to  have  no  effect  upon  the  percentage  of  dot. 
Although  the  stock  never  showed  more  than  50  per  cent  of  dot,  yet 
it  was  found  that  the  normal  individuals  from  the  stock  threw  about 
the  same  per  cent  as  did  those  that  were  dotted,  so  that  the  stock  was 
probably  genetically  pure.  The  number  of  males  which  showed  the 
character  was  always  much  smaller  than  the  number  of  dotted  females; 
in  the  hatches  which  produced  nearly  50  per  cent  of  dot,  nearly  all  the 
females  but  very  few  of  the  males  were  dotted.  Quite  often  t!he  char- 
acter showed  on  only  one  side  of  the  thorax. 

Since  this  character  arose  in  an  experiment  involving  several  eye- 
colors  an  effort  was  made  by  crossing  to  wild  and  extracting  to  transfer 
the  dot  to  flies  normal  in  all  other  respects.  This  effort  succeeded  only 
partly,  for  a  stock  was  obtained  which  differed  from  the  wild  type  only 
in  that  it  bore  dot  (about  30  per  cent)  and  in  that  the  eyes  were  ver- 
milion. Several  attempts  to  get  the  dot  separated  from  vermilion 
failed.  Since  this  was  only  part  of  the  preliminary  routine  work 
necessary  to  get  a  mutant  stock  in  shape  for  exact  experimentation,  no 
extensive  records  were  kept. 

LINKAGE  OF  VERMILION  AND  DOT. 

When  a  dot  male  with  vermilion  eyes  was  bred  to  a  wild  female  the 
offspring  were  wild-type  males  and  females.  These  inbred  gave  the 
data  shown  in  table  19. 

Table  19. — Pi  vermilion  dot  cf   X  zvild  9  9.     Fi  wild-type  9  9 

X  Fi  zvild-type  cf  cf. 


Reference. 

Fj  females. 

Wild-type  cT. 

Vermilion  cf. 

Vermilion 

dot  cf. 

Dot  cf . 

7 

8 

Total . 

345 
524 

151 

24s 

130 
220 

0 
3 

0 
0 

869 

396 

350 

3 

0 

NEW   DATA. 


45 


Only  three  dot  individuals  appeared  in  Fo,  but  since  these  were  males 
the  result  indicates  that  the  dot  character  is  due  to  a  sex-linked  ^en. 
These  three  males  had  also  vermilion  eyes,  indicating  linkaj;e  of  dot  and 
vermilion.  The  males  show  no  deficiency  in  numbers,  therefore  the 
non-appearance  of  the  dot  can  not  be  due  to  its  being  semi-lethal.  It 
appears,  therefore,  that  the  expression  of  the  character  must  depend 
on  the  presence  of  an  intensifying  factor  in  one  of  the  autosomes,  or 
more  probably,  like  club,  it  appears  only  in  a  small  percentage  of  flies 
that  are  genetically  pure  for  the  character. 

The  reciprocal  cross  (dot  female  with  vermilion  eyes  by  wild  male) 
was  made  (table  20).  The  daughters  were  wild  type  and  the  sons 
vermiUon.  Not  one  of  the  272  sons  showed  dot.  If  the  gen  is  sex- 
linked  the  non-appearance  of  dot  in  the  Fi  males  can  be  explained 
on  the  ground  that  males  that  are  genetically  dot  show  dot  very  rarely, 
or  that  its  appearance  is  dependent  upon  the  intensification  by  an 
autosomal  factor  of  the  effect  produced  by  the  sex-linked  factor  for  dot. 

Table  20. — Pi  vermilion  dot  9  X  ^vild  cf . 


First  generation. 

Second  generation. 

Reference. 

Wild- 
type 

9. 

Ver- 
milion 

Reference. 

Wild- 
type 
9. 

Wild-    Ver- 
tvpe    milion 

d'.  !   9. 

Ver-  ;  Ver- 
milion milion 

d.    dot  9. 

Ver- 
milion 
dot  cf. 

Dot 

9. 

Dot 

d'. 

137  c... 

138C. ... 
Total . 

44         45 

77        62 

124   ;      124 

57         41 

19 

22 

28 

Total . 

211 

266 
143 

198     228 
220    227 
149  1   125 

206       20 
227       16 
124       14 

3 
0 

I 

0 
0 
0 

0 
0 
0 

620 

567 

570 

557 

50 

4 

0 

0 

291  1     272 

The  F2  generation  is  given  in  table  20.  The  dot  reappeared  in  V> 
both  in  females  and  in  males,  but  instead  of  appearing  in  50  per  cent  of 
both  sexes,  as  expected  if  it  is  simply  sex-linked,  it  appeared  in  4.0  per 
cent  in  the  females  and  in  only  0.4  per  cent  in  the  males.  The  failure 
of  the  character  to  be  fully  realized  is  again  apparent,  but  here,  where 
it  is  possible  for  it  to  be  realized  equally  in  males  and  females,  we  find 
that  there  are  50  females  with  dot  to  only  4  dot  males.  1  his  would 
indicate  that  the  character  is  partially  ''sex-limited''  (Morgan,  I9I4(/) 
in  its  realization.  The  dot  appeared  only  in  flies  with  vermilion  eyes, 
indicating  extremely  strong  linkage  between  vermilion  and  dot. 

The  evidence  from  the  history  of  the  stock,  together  with  these 
experiments,  shows  that  the  character  resembles  club  (wing)  in  that  it 
is  not  expressed  somatically  in  all  the  flies  which  are  homozygous  for  it. 
In  the  case  of  club  we  were  fortunate  enough  to  find  a  constant  feature 


46 


SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 


which  we  could  use  as  an  index,  but,  so  far  as  we  have  been  able  to  see, 
there  is  no  such  constant  accessory  character  in  the  case  of  the  dot. 
Unlike  club,  dot  is  markedly  sex-limited  in  its  effect;  that  is,  there  is 
a  difference  of  expression  of  the  gen  in  the  male  and  female.  This 
difference  recalls  the  sexual  dimorphism  of  the  eosin  eye. 

BOW. 

In  an  Fo  generation  from  rudimentary  males  by  wild  females  there 
appeared,  August  15,  191 2,  a  single  male  whose  wings  instead  of  being 
flat  were  turned  down  over  the  abdomen  (fig.  c).  The  curvature  was 
uniform  throughout  the  length  of  the  wing.  A  previous  mutation,  arc, 
of  this  same  type  had  been  found  to  be  a  recessive  character  in  the 
second  group.  The  new  mutation,  bow,  is  less  extreme  than  arc  and 
is  more  variable  in  the  amount  of  curvature.  When  the  bow  male  was 
mated  to  wild  females  the  offspring  had  straight  wings. 


Fig.  C. — Bow  wing. 


Table  21.— Pi  bow  d'd'  X  zvild  9  9 


First  generation. 

Second  generation. 

Reference. 

Wild-type 
99. 

Wild-type 

Reference. 

Wild-type 
9  9. 

Wild-type 

Bow 

cfcT. 

169  C. . . 

17 

17 

18I 

21  I 

Total . 

193 
182 

145 

100 

67 

49 

375 

245 

116 

NEW    DATA. 


47 


The  F2  ratio  in  table  21  is  evidently  the  2:1:1  ratio  typical  of  sex- 
linkage,  but  with  the  bow  males  running  behind  expectation.  This 
deficiency  is  due  in  part  to  viability  but  more  to  a  failure  to  recognize 
all  the  bow-winged  individuals,  so  that  some  of  them  were  classified 
among  the  not-bow  or  straight  wings.  In  favor  of  the  view  that  the 
classification  was  not  strict  is  the  fact  that  the  sum  of  the  two  male 
classes  about  equals  the  number  of  the  females. 

BOW  BY  ARC. 

When  this  mutant  first  appeared  its  similarity  to  arc  led  us  to  suspect 
that  it  might  be  arc  itself  or  an  allelomorph  of  arc.  It  was  bred,  there- 
fore, to  arc.  The  bow  male  by  arc  females  gave  straight  (normal) 
winged  males  and  females.  The  appearance  of  straight  wings  shows 
that  bow  is  not  arc  nor  allelomorphic  to  arc.  When  made  later,  the 
reciprocal  cross  of  bow  female  by  arc  male  gave  in  Fi  straight-winged 
females  but  bow  males.  This  result  is  in  accordance  with  the  inter- 
pretation that  bow  is  a  sex-Hnked  recessive.  Further  details  of  these 
last  two  experiments  may  now  be  given.  The  Fi  (wild-type)  flies  from 
bow  male  by  arc  female  were  inbred.     The  data  are  given  in  table  22. 

Table  22. — Pi  bou;  d^  X  arc  9  . 


First  generation. 

Second  generation. 

Reference. 

Wild-type 

9  9. 

Wild-tvpe 

Reference. 

Straight. 

Not- 
straight. 

71  c... 

75  C.  .  .  . 
Total . 

48 
28 

43 

27 

71C.... 

179 

133 

76 

70 

Bow  and  arc  are  so  much  alike  that  they  give  a  single  rather  variable 
phenotypic  class  in  F2.  Therefore  the  F2  generation  is  made  up  of  only 
two  separable  classes — flies  with  straight  wings  and  flies  with  not- 
straight  wings.  The  ratio  of  the  two  should  be  theoretically  9 :  7, 
which  is  approximately  realized  in  179:  133- 

If  the  distribution  of  the  characters  according  to  sex  is  ignored,  the 
case  is  similar  to  the  case  of  the  two  white  races  of  sweet  peas,  which 
bred  together  gave  wild-type  or  purple  peas  in  Fi  and  in  F-..  gave  9 
colored  to  7  white.  If  sex  is  taken  into  account,  the  theoretical  expec- 
tation for  the  F2  females  is  6  straight  to  2  arc,  and  for  the  Y2  males  3 
straight  to  i  arc  to  3  bow  to  i  bow-arc. 

The  Fi  from  bow  females  by  arc  male  and  their  F2  oft'spring  arc  given 
in  table  23. 


48 


SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 


Table  23. — Pi  bow  9  X  arc  d^. 


First  generation. 

Second  generation. 

Reference. 

Wild-type 
9  9. 

Bow  cf  cf- 

Reference. 

Straight. 

Not- 
straight. 

72  C... 
73C.... 

5I.... 
74C.... 

Total . 

22 
12 
22 
S6 

19 
10 
21 

52 

3I.... 
3.1I.... 

5.1I.... 

Total . 

56 
46 

90 

69 

62 

68 

108 

112 

102 

248 

307 

In  this  case  the  F2  expectation  is  6  straight  to  10  not-straight.  Since 
the  sex-Hnked  gen  bow  entered  from  the  female,  half  the  F2  males 
and  females  are  bow.  The  half  that  are  not-bow  consist  of  3  straight  to 
I  arc,  so  that  both  in  the  female  classes  and  in  the  male  classes  there 
are  3  straight  to  5  not-straight  or  in  all  6  straight  to  10  not-straight. 
The  realized  result,  248  straight  to  307  not-straight,  is  more  nearly  a 
3  :  4  ratio,  due  probably  to  a  wrong  classification  of  some  of  the  bow  as 
straight. 

LEMON  BODY-COLOR. 

(Plate  I,  figure  3.) 

A  few  males  of  a  new  mutant  with  a  lemon-colored  body  and  wings 
appeared  in  August  1912.  The  lemon  flies  (Plate  II,  fig.  3)  resemble 
quite  closely  the  yellow  flies  (Plate  II,  fig.  4).  They  are  paler  and  the 
bristles,  instead  of  being  brown,  are  black.  These  flies  are  so  weak 
that  despite  most  careful  attention  they  get  stuck  to  the  food,  so  that 
they  die  before  mating.  The  stock  was  at  first  maintained  in  mass 
from  those  cultures  that  gave  the  greatest  percentage  of  lemon  flies. 
In  a  few  cases  lemon  males  mated  with  their  gray  sisters  left  off'spring, 
but  the  stock  obtained  in  this  way  had  still  to  be  maintained  by  breeding 
heterozygotes,  as  stated  above.  But  from  the  gray  sisters  heterozygous 
for  lemon  (bred  to  lemon  males)  some  lemon  females  were  also  produced. 

LINKAGE  OF  CHERRY,  LEMON,  AND  VERMILION. 

In  order  to  study  the  linkage  of  lemon,  the  following  experiment  was 
carried  out.  Since  it  was  impracticable  to  breed  directly  from  the 
lemon  flies,  virgin  females  were  taken  from  stock  throwing  lemon,  and 
were  mated  singly  to  cherry  vermilion  males.  Only  a  few  of  the  females 
showed  themselves  heterozygous  for  lemon  by  producing  lemon  as  well 
as  gray  sons.  Half  the  daughters  of  such  a  pair  are  expected  to  be 
heterozygous  for  lemon  and  also  for  cherry  and  vermilion,  which  went 
in  from  the  father.  These  daughters  were  mated  singly  to  cherry 
vermilion  males,  and  those  that  gave  some  lemon  sons  were  continued. 


NEW    DATA. 


49 


and  are  recorded  in  table  24.     The  four  classes  of  females  were  not 
separated  from  each  other,  but  the  total  of  females  is  given  in  the  table. 

Table  24. — Pj  lemon  (hei.)  9  X  cherry  vermilion  cf  cf .     Fi  zcild-type  9  X 

cherry  vermilion  cf  d^. 


Females. 

WC 

V 

!  w^i 

in 
V 

1 

-4- 

u.     V 

W^.!,,, 

,v 

Total 

l.n 

'  1 

■T^ 

r>.            1 

Cherry 

ver- 
milion. 

Lemon. 

Cherry 
lemon. 

Ver- 
milion. 

Cherry. 

Lemon 

ver- 
milion. 

Cherry 

lemon 

vermilion. 

Wild 
type. 

O'er. 

71 

42 

19 

2 

6 

3 

6 

0 

0 

78 

88 

26 

19 

2 

8 

8 

4 

0 

0 

67 

36 

28 

7 

0 

2 

1 

0 

0 

0 

38 

SI 

12 

22 

0 

4 

4 

4 

0 

0 

46 

98 

29 

35 

0 

8 

s     , 

I 

0 

0 

78 

47 

17 

II 

0 

I 

3       1 

2 

0 

0 

34 

46 

23 

20 

I 

6 

3 

2 

0 

0 

57 

437 

177 

133 

S 

35 

29 

19 

0 

0 

398 

There  are  three  loci  involved  in  this  cross,  namely,  cherry,  lemon,  and 
vermilion.  Of  these  loci  two  were  known,  cherry  and  vermilion.  The 
data  are  consistent  with  the  assumption  that  the  lemon  locus  is  between 
cherry  and  vermilion,  for  the  double  cross-over  classes  (the  smallest 
classes)  are  cherry  lemon  vermilion  and  wild  type.  The  number  of 
smgle  cross-overs  betw^een  cherry  and  lemon  and  between  lemon  and 
vermilion  are  also  consistent  with  this  assumption.  Since  lemon  flies 
fail  to  emerge  successfully,  depending  in  part  upon  the  condition  of  the 
bottle,  the  classes  involving  lemon  are  worthless  in  calculating  crossing- 
over  and  are  here  ignored.  In  other  words,  lemon  may  be  treated  as 
though  it  did  not  appear  at  all,  i.  e.y  as  a  lethal.  The  not-lemon 
classes — cherry,  vermilion,  cherry  vermilion,  and  wild  type — give  the 
following  approximate  cross-over  values  for  the  three  loci  involved: 
Cherry  lemon,  15;  lemon  vermilion,  12;  cherry  vermilion,  27.  I  he 
locus  of  lemon,  calculated  by  interpolation,  is  at  about  17.5 

LETHAL  2. 

In  September  191 2  a  certain  wild  female  produced  78  daughters  and 
only  16  sons  (Morgan,  1914Z');  63  of  these  daughters  were  tested  and 
31  of  them  gave  2  females  to  i  male,  while  ^z  of  them  gave  i  :  i 
sex-ratios.  This  shows  that  the  mother  of  the  original  high  sex-ratio 
was  heterozygous  for  a  recessive  sex-linked  lethal.  In  order  to  deter- 
mine the  position  of  this  lethal,  a  lethal-bearing  female  was  bred  to  an 
eosin  (or  white)  miniature  male,  and  those  daughters  that  were  hetero- 
zygous  for  eosin,   lethal,   and   miniature  were   then   b;ick-crossed   to 


50 


SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 


eosin  miniature  males.  The  daughters  that  result  from  such  a  cross 
give  only  the  amount  of  crossing-over  between  eosin  and  miniature 
(as  29.7),  but  the  males  give  the  cross-over  values  for  eosin  lethal  (9.9), 
lethal  miniature  (15.4),  and  eosin  miniature  (25.1).  The  data  for  this 
cross  are  given  in  table  25. 

T.-VBLE  25. —  Total  data  upon  linkage  of  eosin,  lethal  2,  and  miniature,  from 

Morgan,  igi4.b. 


'emales. 


Total. 


Cross- 
overs. 


cross- 
over 
value 


Males. 


W^   m  wMo      w^' 


w^   lo  m 


Cross-over  values. 


m 


lo  m 


4-^+- 


Eosin 
lethal  2. 


Lethal  2 
miniature. 


Eosin 
miniature. 


15,904 


4,736  j  29.7 


5.045 


653 


1,040 


14 


9  9 


15  4 


A  similar  experiment,  in  which  eosin  and  vermilion  were  used  instead 
of  eosin  and  miniature,  is  summarized  in  table  26. 

Table  26. — Total  data  upon  the  linkage  of  eosin,  lethal  2,  and  vermilion,  from 

Morgan,  igi^b. 


Females.             \                                                      Males. 

Total. 

Cross- 
overs. 

1 

Cross- ^e       y 

W^  I5        W^ 

w^  !„    V 

Cross-over  values. 

Eosin 
lethal  2. 

Lethal  2         Eosin 
vermilion,    vermilion. 

value.        *2 

V         I2    V 

2,656 

729 

j 
275  i     902 

124 

227 

6 

10.3 

18.5             27.9 

I 

Considerable  data  in  which  lethal  was  not  involved  were  also  obtained 
in  the  course  of  these  experiments  and  are  included  in  the  summary  of 
the  total  data  given  in  table  27. 

Table  27. — Summary  of  all  data  upon  lethal  2,  fro?n  Morgan,  iQi4b. 


Gens. 

Total. 

Cross-overs. 

Cross-over 
values. 

White  lethal  2 

White  vermilion 

8,011 
6,023 
36,021 
1,400 
6,752 

767 
1,612 

1 1 , 048 

248 

1,054 

9.6 

26.8 
30.7 
177 
15  4 

White  miniature 

Leth:il   2  vermilion 

Lethal   2  miniature 

The  amount  of  crossing-over  between  eosin  and  lethal  is  about  10  per 
cent  and  the  amount  of  crossing-over  between  lethal  and  miniature  is 
about  18  per  cent.     Since  the  amount  of  crossing-over  between  eosin 


NEW    DATA. 


SI 


and  miniature  is  over  30  per  cent,  the  lethal  factor  must  lie  between 
eosin  and  miniature,  somewhat  nearer  to  eosin.  It  is  impossible  at 
present  to  locate  lethal  2  accurately  because  of  a  real  discrepancy  in 
the  data,  which  makes  it  appear  that  lethal  2  extends  for  a  distance 
of  about  5  units  along  the  chromosome  from  about  10  to  about  15. 
Work  is  being  done  which  it  is  hoped  will  make  clear  the  reason  for 
this.  For  the  present  we  may  locate  lethal  2  at  the  midpoint  of  its 
range,  or  at  12.5. 

CHERRY. 

(Plate  II,  figure  9.) 

The  origin  of  the  eye-color  cherry  has  been  given  by  Safir  (Biol. 
Bull.,  1913). 

Cherry  appeared  (October  191 2)  in  an  experiment  involving  vermilion 
eye-color  and  miniature  wings.  This  is  the  only  time  the  mutant  has 
ever  come  up,  and  although  several  of  this  mutant  (males)  appeared 
in  Safir's  experiment,  they  may  have  all  come  from  the  same  mother. 
It  is  probable  that  the  mutation  occurred  in  the  vermilion  stock  only  a 
generation  or  so  before  the  experiment  was  made,  for  otherwise  cherry 
would  be  expected  to  be  found  also  in  the  vermilion  stock  from  which 
the  mothers  were  taken;  however,  it  was  not  found. 

A  SYSTEM  OF  QUADRUPLE  ALLELOMORPHS. 

Safir  has  described  crosses  between  this  eye-color  and  red,  white, 
eosin,  and  vermiHon.  We  conclude  for  reasons  similar  to  those  given 
by  Morgan  and  Bridges  (Jour.  Exp.  Zool.,  1913)  for  the  case  of  white 
and  eosin,  that  cherry  is  an  allelomorph  of  white  and  of  eosin.  This  is 
not  the  interpretation  followed  in  Safir's  paper,  where  cherry  is  treated 
as  though  absolutely  linked  to  white  or  to  eosin.  Both  interpretations 
give,  however,  the  same  numerical  result  for  each  cross  considered  by 
itself.  Safir's  data  and  those  which  appear  in  this  paper  show  that 
white,  eosin,  cherry,  and  a  normal  (red)  allelomorph  form  a  system  of 
quadruple  allelomorphs.  If  this  interpretation  is  correct,  then  the 
linkage  relations  of  cherry  should  be  identical  with  those  of  white  or  of 
eosin. 

LINKAGE  OF  CHERRY  AND  VERMILION. 

The  cross-over  value  for  white  (eosin)  and  vermilion,  based  on  a 
very  large  amount  of  data,  is  about  31  units.  An  experiment  of  our 
own  in  which  cherry  was  used  with  vermilion  gave  a  cross-over  value 
of  31  units,  which  is  a  close  approximation  to  the  cross-over  value  of 
white  and  vermilion.  The  cross  which  gave  this  data  was  that  ot  a 
cherry  vermilion  (double  recessive)  male  by  wild  females.  1  he  I'l 
wild-type  flies  inbred  gave  a  single  class  of  females  (wild-type)  and  the 
males  in  four  classes  which  show  by  the  deviation  from  a  1:1:1:1 
ratio  the  amount  of  crossing-over  involved. 


52 


SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 


In  one  of  the  Fo  male  classes  of  table  28  the  simple  eye-color  cherry 
appeared  for  the  first  time  (since  the  original  mutant  was  vermilion  as 
well  as  cherry).     Safir  has  recorded  a  similar  cross  with  like  results. 

Table   28. — Pi  cherry  vermilion   cf  d^   X  zt'ild    9  9-      Fi  wild-type   9  9 

X  Fi  zc'ild-type  cf  cf  • 


Reference. 

Wild- 
type  9  9  • 

Non-cross-over  cT. 

Cross-over  c?. 

Total. 

Cross- 
over 
value. 

Cherry 

ver- 
milion. 

Wild- 
type. 

Cherry. 

Ver- 
milion. 

160C 

188 
256 
251 
229 

57 
8S 
78 
76 

61 

93 
78 
95 

32 
40 
20 
34 

34 
52 
37 
33 

184 

270 
213 
238 

36 

34 

26 
28 

161C 

162  C 

163  C 

Total 

924 

296 

327 

126 

156 

905 

31 

Some  cherry  males  were  bred  to  wild  females.  The  Fi  wild-type 
males  and  females  inbred  gave  the  results  shown  in  table  29.  Some  of 
the  cherry  males  thus  produced  were  bred  to  their  sisters.  Cherry 
females  as  well  as  males  resulted;  and  it  was  seen  that  the  eye-color  is 
the  same  in  the  males  and  females,  in  contradistinction  to  the  allelo- 
morph eosin,  where  there  is  a  marked  bicolorism  (figs.  7,  8,  Plate  II). 
The  cherry  eye-color  is  almost  identical  with  that  of  the  eosin  female, 
but  is  perhaps  slightly  more  translucent  and  brighter. 

Table  29. — Pi  cherry  cT  cT  X  wild  9  9.     Fi  wild-type  9  9  X  Pi  wild-typed^  o^. 


Reference. 

Wild-type  9  • 

Wild-type  cf . 

Cherry  cf . 

15I 

266 

120 

100 

COMPOUNDS  OF  CHERRY. 

In  order  to  examine  the  effect  of  the  interaction  of  cherry  and  white 
in  the  same  individual  (i.  e.,  white-cherry  compound)  cherry  females 
were  crossed  to  white  males.  This  cross  should  give  white-cherry 
females  and  cherry  males.  These  white-cherry  females  were  found 
(table  30)  to  be  very  much  lighter  than  their  brothers,  the  cherry  males. 
The  color  of  the  pure  cherry  females  and  males  is  the  same,  but  the 
substitution  of  one  white  for  one  cherry  lowers  the  eye-color  of  the 
female  below  that  of  the  cherry  male.  In  eosin  the  white  also  lowers 
the  eye-color  of  the  compound  female  about  in  the  same  proportion  as 
in  the  case  of  cherry.  In  the  eosin  the  female  starts  at  a  higher  degree 
of  pigmentation  than  the  male  and  dilution  seems  to  bring  her  down 


NEW    DATA. 


3^ 


to  the  level  of  the  male.  But  this  coincidence  of  color  between  eosin 
male  and  white-eosin  compound  female  is  probably  without  significance, 
as  shown  by  the  results  with  cherry. 

Table  30.— Pi  cherry  9  9   X  white  d^  d" . 


Reference. 

First  generation. 

White-cherry 
compound  9 . 

Cherry  d^. 

9M 

321 

302 

Eosin-cherry  compound  was  also  made.  An  eosin  female  was  mated 
to  a  cherry  male.  The  eosin-cherry  daughters  were  darker  than  their 
eosin  brothers.     Inbred  they  gave  the  results  shown  in  table  31. 

Table  31. — Pi  eosin  9   X  cherry  cf . 


First  generation. 

Second  generation. 

Reference. 

Eosin-cherry 
compound 

9  9. 

Eosin  cf  cf. 

Reference. 

Eosin  and 

eosin-cherry 

compound  9  9- 

Cherry  cf. 

Eosin  (f. 

43  C 

71 

58 

I  I 

2I 

154 
174 

99 
74 

62 

77 

328 

173 

139 

Although  in  the  F2  results  there  are  two  genotypic  classes  of  females, 
namely,  pure  eosin  and  eosin-cherry  compound,  the  eye-colors  are  so 
nearly  the  same  that  they  can  not  be  separated.  The  two  classes  of 
males  can  be  readily  distinguished;  of  these,  one  class,  cherry,  has  the 
same  color  as  the  females,  while  the  other  class,  eosin,  is  much  lighter. 
Such  an  F2  group  will  perpetuate  itself,  giving  one  type  of  female  (of 
three  possible  genotypic  compositions,  but  somatically  practically 
homogeneous)  and  two  types  of  males,  only  one  of  which  is  like  the 
females. 

FUSED. 

In  a  cross  between  purple-eyed^  males  and  black  females  there  ap- 
peared in  F2  (Nov.  4,  191 2)  a  male  having  the  veins  of  the  wing 
arranged  as  shown  in  text-figure  D  b.  It  will  be  seen  that  the  third  and 
the  fourth  longitudinal  veins  are  fused  from  the  base  to  and  beyond  the 

'Purple  is  an  eye-color  whose  gen  is  in  the  second  chromosome. 


54 


SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 


point  at  which  in  normal  flies  the  anterior  cross-vein  lies.  The  cross- 
vein  and  the  cell  normally  cut  off  by  it  are  absent.  There  are  a  number 
of  other  features  (see  fig.  D  c)  characteristic  of  this  mutation:  the  wings 
are  held  out  at  a  wide  angle  from  the  body,  the  ocelli  are  very  much 
reduced  in  size  or  entirely  absent,  the  bristles  around  the  ocelli  are 
usually  small.  The  females  are  absolutely  sterile,  not  only  with  their 
own,  but  with  any  males. 

Fused  males  by  wild  females  gave  wild-type  males  and  females. 
Inbred  these  gave  the  results  shown  in  table  32.  The  fused  character 
reappeared  only  in  the  Fo  males,  showing  that  it  is  a  recessive  sex- 
linked  character. 

Table  32.— Pi  fused  &  X  zvild  9  9  . 


First  generation. 

Second  generation. 

Reference. 

Wild-type 
9  9. 

Wild-type 

Reference. 

Wild-type 

9  9. 

Wild-type 

cfcf. 

Fused  cfcf. 

4I 

66 

43 

190  C 

14I 

Total 

258 
239 

96 

105 

"5 

90 

497 

201 

205 

The  reciprocal  cross  was  tried  many  times,  but  is  impossible,  owing 
to  the  sterility  of  the  females.  Since  the  fused  females  are  sterile  to 
fused  males,  the  stock  is  kept  up  by  breeding  heterozygous  females  to 
fused  males. 

By  means  of  the  following  experiments  the  position  of  fused  in  the 
X  chromosome  was  determined.  A  preliminary  test  was  made  by 
mating  with  eosin,  whose  factor  lies  near  the  left  end  of  the  X  chromo- 
some series. 

LINKAGE  OF  EOSIN  AND  FUSED. 

Fused  (red-eyed)  males  mated  to  eosin  (not-fused)  females  gave  wild- 
type  daughters  and  eosin  sons,  which  inbred  gave  the  classes  shown  in 
table  33. 

Table  33. — Pj  eosin  9  9   X  fused  cf  cf .     Fj  tvild-type  9  9   X  Fi  eosin  cf  cT- 


Reference. 

Females. 

Non-cross-over  d'cf. 

Cross-over  cf  cf  • 

Total 
males. 

Cross- 
over 
value. 

Eosin. 

Fused. 

Eosin  fused. 

Wild-type. 

S6I 

496 

131 

113 

82 

104 

430 

43 

NEW    DATA. 


33 


The  data  give  43  per  cent  of  crossing-over,  which  places  fused  far  to 
the  right  or  to  the  left  of  eosin.  The  latter  position  is  improhable, 
since  eosin  already  lies  very  near  the  extreme  left  end  of  the  known 
series.  Therefore,  since  43  per  cent  would  place  the  factor  nearly  at 
the  right  end  of  the  series,  the  next  step  was  to  test  its  relation  to  a 
factor  Hke  bar  that  lies  at  the  right  end  of  the  chromosome.  By  mating 
to  bar  alone  we  could  only  get  the  linkage  to  bar  without  discovering  on 


Fig.  D. — a,  normal  wing;  b  and  c,  fused  wings,  c  shows  a  typical  fused  wing.  The  nio-<t  !»trikinK 
feature  is  the  closure  of  the  cell  between  the  third  and  fourth  longitudinal  veins  with  the 
elimination  of  the  cross-vein;  the  veins  at  the  base  of  the  wing  differ  from  those  in  the  normal 
shown  in  a.  b  shows  the  normal  po.sition  in  which  the  fused  wings  arc  held.  The  fusion  of 
the  veins  in  b  is  unusually  complete. 

which  side  of  bar  the  new  factor  lies,  but  by  mating  to  a  Hy  that  carries 
still  another  sex-linked  factor,  known  to  lie  to  the  left  of  bar,  the  infor- 
mation gained  should  show  the  relative  order  of  the  factors  involved. 
Furthermore,  since,  by  making  a  back-cross,  both  males  and  females 
give  the  same  kind  of  data  (and  need  not  be  separated),  the  experiment 
was  made  in  this  way.  In  order  to  have  material  for  sucii  an  experi- 
ment double  mutant  stocks  of  vermilion  fused  and  also  of  bar  fused 
were  made  up. 


56 


SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 


LINKAGE  OF  VERMILION,  BAR,  AND  FUSED. 

Males  from  the  stock  of  (red)  bar  fused  were  mated  to  vermilion 
(not-bar,  not-fused)  females,  and  produced  bar  females  and  vermilion 
males.  The  bar  Fi  daughters  were  back-crossed  to  vermilion  fused 
males  and  produced  the  classes  of  offspring  shown  in  table  34. 

Table  34. — Pi  zermilion  9  9   X  bar  fused  cf  cT.      B.C.  Fibar  9   X  vermilion 

fused  cf  cf- 


V 

B'fu 

V     B'  f„ 

V 

B 

^ 

v^ 

■^ 

Total. 

Cross 

-over  values. 

Reference. 

Ver- 
milion. 

Bar 
fused. 

Ver- 
milion 

bar 
fused. 

Wild- 
type. 

Ver- 
milion 
fused. 

Bar. 

Ver- 
milion 
bar. 

Fused. 

Ver- 
milion 
bar. 

Bar 
fused. 

Ver- 
milion 
fused. 

140  I... 

137 

130 

35 

40 

5 

8 

355 

21 

4 

25 

141  I. 

* 

^    144 

137 

38 

41 

4 

2 

366 

22 

2 

23 

142  I. 

*i 

153 

120 

43 

58 

6 

7 

I 

388 

26 

4 

29 

143  I. 

153 

92 

44 

41 

3 

7 

3 

I 

344 

26 

4 

28 

145  I. 

69 

62 

29 

19 

I 

I 

181 

27 

I 

27 

146  I. 

96 

103 

30 

34 

7 

3 

273 

23 

4 

26 

156  1. 

62 

45 

25 

27 

I 

4 

. . 

164 

32 

3 

35 

157  I. 

93 

57 

II 

31 

2 

2 

2 

198 

22 

3 

23 

Tot: 

i\. 

907 

746 

255 

291 

29 

33 

5 

3 

2,269 

24 

3 

27 

The  data  show  that  the  factor  for  fused  lies  about  3  units  to  the  right 
of  bar.  This  is  the  furthest  point  yet  obtained  to  the  right.  The 
reasons  for  locating  fused  to  the  right  of  bar  are  that,  if  it  occupies  such 
a  position,  then  the  double  cross-over  classes  (which  are  expected  to  be 
the  smallest  classes)  should  be  vermilion  bar  and  fused,  and  these  are, 
in  fact,  the  smallest  classes.  The  order  of  factors  is,  then,  vermilion, 
bar,  fused.  This  order  is  confirmed  by  the  result  that  the  number  of 
cross-overs  between  fused  and  vermilion  is  greater  than  that  between 
bar  and  vermilion. 

In  order  to  obtain  data  to  balance  viability  effects,  the  following 
experiment  was  made: 

Vermilion  (not-bar)  fused  males  were  bred  to  (red)  bar  (not-fused) 
females.  The  daughters  and  sons  were  bar.  The  daughters  were 
back-crossed,  singly,  to  vermilion  fused  males  and  gave  the  results 
shown  in  table  3  5.  Each  female  was  also  transferred  to  a  second  culture 
bottle,  so  that  for  each  female  there  are  two  broods  given  consecutively 
(82,  82',  etc.)  in  table  35. 

The  results  given  by  the  two  broods  of  the  same  female  are  similar. 
The  values  are  very  near  to  those  given  in  the  last  experiment,  and 
confirm  the  conclusions  there  drawn.  The  combined  data  give  the 
results  shown  in  table  36. 


NEW    DATA. 


57 


Table  35. — Pi  bar  9  9  X  vermilion  fused  cfcf .     B.  C.  Fi  bar  9  X  vermilion 

fused  cp  cf  ■ 


Reference. 

V 

fu 

V      B' 

V 

V 

.B' 

fu 

Total. 

B' 

'        fu 

B'"fu 

— 1 1 — 

Cross-over  values. 

Ver- 
milion 
fused. 

Bar. 

Ver- 
milion 
bar. 

Fused. 

Ver- 
milion. 

Bar 

fused. 

Ver- 
milion 

bar 
fused. 

Wild- 
type. 

Ver- 
milion 
bar. 

Bar 

fused. 

Ver- 
milion 
fused. 

82 

82' 

83 

83' 

89 

89' 

90 

90' 

91 

91' 

92 

92' 

93 

93' 

94 

94' 

95 

96 

97 

98 

Firsts. . . 
Seconds . 

Total . 

i6s 

104 
128 
100 

85 
78 
86 

33 
125 

91 
109 

100 

75 
68 

84 
61 

84 
144 

81 

107 

1,273 

635 

i6s 

87 

164 

94 

105 

91 

85 

38 

107 

95 
136 
105 

67 

94 
96 

73 
102 
148 

96 

112 

1.383 

677 

63 
26 

51 

28 

23 
21 

30 

22 

41 
31 
41 
29 
19 
31 
31 
20 

27 
43 
25 
39 
433 
208 

57 
24 
39 
30 
24 
27 
28 
14 
31 

25 

24 
29 
20 
17 

35 
22 
26 

34 
20 

33 
371 
188 

8 

6 
4 

5 

I 

5 
4 

I 

5 
4 

I 

8 

5 
3 

I 

5 

I 

47 

20 

7 
4 
4 
4 

2 

2 

I 
I 

I 
2 

I 
I 
I 
I 

4 

3 
2 

3 

2 

28 

18 

I 

* 

I 

5 

466 

245 
392 
260 

244 
221 

234 
"3 

306 
250 
316 
265 
182 
212 

255 
1 8s 

245 

373 
230 

294 
3.537 
1.75 1 

26 
20 
23 

22 

19 

22 

25 

33 
24 
23 
21 
22 
21 

23 
26 

23 
22 
21 

20 
25 
23 
23 

3 
2 

3 
3 
3 

2 
2 

S 

I 

3 
2 

I 
I 
I 
4 
5 
2 
I 

4 

I 
2 
3 

29 

22 
26 

25 

22 
23 
27 
36 

24 

25 

23 

22 
22 

24 
29 
28 

24 
21 

23 
26 

25 
25 

1,908 

2,060 

641 

559 

67 

46 

I 

6 

5,288 

23 

2.3 

25 

Table  36. — Linkage  of  vermilion,  bar,  and  fused  with  balanced  viability. 


Percentage.  .  . 


B'fu 


5,621 

74-3 


B'fu 


1,756 
23.19 


V  B' 


fu 


17s 

2.31 


^ 


fu 


15 

0.2 


Tot 


ai. 


7,567 


Some  additional  data  bearing  on  the  linkage  of  vermilion  and  fused 
were  obtained.  Males  of  (red)  fused  stock  were  bred  to  vermilion 
(not-fused)  females,  and  gave  wild-type  females  and  vermilion  males, 
which  inbred  gave  the  results  shown  in  table  37. 

The  percentage  of  cross-overs  between  vermilion  and  fused  is  here  27, 
which  is  in  agreement  with  the  26  per  cent  of  the  preceding  expermient. 

The  converse  experiment,  namely,  red  (not-fused)  temaks  by 
vermilion  fused  males  also  gave,  when  the  wild-type  daugiiters  were 


58 


SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 


back-crossed  to  vermilion  fused  males,  a  linkage  value  of  27  units. 
Two  lo-day  broods  were  reared  from  each  female.  The  data  given  in 
table  38  show  that  the  percentage  of  crossing-over  does  not  change  as 
the  flies  get  older.  The  locus  of  fused  on  the  basis  of  all  of  the  data  is 
at  59.5. 

Table  37. — Pj  vermilion  9  9  X  fused  cf  cf .     Fi  wild-type  9  9 

X  Fi  vermilion  cf  cf  • 


Reference. 

Females. 

Non-cross-over  cf  cf . 

Cross-over  cf  cf. 

Total 

cTd^. 

Cross- 
over 
values. 

Vermilion. 

Fused. 

Vermilion 
fused. 

Wild- 
type. 

79I 

80  I 

81  I 

Total . 

299 

245 
263 

93 
93 

lOI 

96 

60 
63 

37 
28 
22 

36 
27 
40 

262 
208 
226 

28 
26 
27 

807 

287 

219 

87 

103 

696 

27 

Table  38. — Pi  wild  9  9    X  vermilion  fused  cf  cf .     F\  wild-type  9 

X  Fi  wild-type  cf  cf . 


Reference. 

Wild- 
type 
9  9. 

Non-cross-over  cf. 

Cross-over  cf. 

Total 

cfcf. 

Cross- 
over 
values. 

Vermilion 
fused. 

Wild- 
type. 

Vermilion. 

Fused. 

52 

52' 

S3 

S3' 

54 

54' 

57 

57' 

58 

58' 

Firsts.  .  . . 
Seconds. . 

Total . 

96 

176 

60 

76 

88 

60 

61 

170 

128 

144 

433 
626 

25 

59 
20 
21 

35 
22 
22 
47 
37 
38 
139 
187 

30 
64 
22 

27 
38 
20 
20 
54 
55 
64 
i6s 
229 

16 

24 

9 

II 

14 

8 

7 
24 

14 
16 
60 
83 

II 

19 

6 

10 

16 

9 
II 

19 

10 

15 
54 
72 

82 
166 

57 
69 

103 

59 

60 

144 

116 

133 
418 
571 

33 
26 
26 
31 
29 
29 
30 
30 
21 
23 
27 
27 

1. 059 

326 

394 

H3 

126 

989 

27 

FORKED. 

On  November  19,  191 2,  there  appeared  in  a  stock  of  a  double 
recessive  eye-color,  vermilion  maroon,  a  few  males  which  showed  a 
novel  form  of  the  large  bristles  (macrochaetae)  upon  the  head  and 
thorax.  In  this  mutation  (text-fig.  e)  the  first  of  several  which  affect 
the  shape  and  distribution  of  the  bristles,  the  macrochaetae,  instead  of 


I 


NEW    DATA. 


59 


being  long,  slender,  and  tapered  (see  Plate  I,  fig.  i),  are  greatly  shortened 
and  crinkled  as  though  scorched.  The  ends  are  forked  or  branched, 
bent  sharply,  or  merely  thickened.  The  bristles 
which  are  most  disorted  are  those  upon  the 
scutellum,  where  they  are  sometimes  curled 
together  into  balls. 

LINKAGE  OF  VERMILION  AND  FORKED. 

Since  forked  arose  in  vermilion  stock,  the 
double  recessive  for  these  two  sex-linked  fac- 
tors could  be  used  in  testing  the  linkage  rela- 
tions of  the  mutation.  Vermilion  forked  males 
were  crossed  to  wild  females  and  gave  wild- 
type  males  and  females,  which  inbred  gave 
in  F2  the  results  shown  in  table  39.  Forked 
reappeared  only  in  the  males  in  the  following 
proportion:  not-forked  9,742;  not-forked  c?*,  ^'^  e. 
346;  forked  cf,  301.  The  result  shows  that  the  character  is  a  se.x- 
linked  recessive. 

Table  39. — Pi  wild  9  9  X  vermilion-jorked  cf  cf .     Fi  ivild-type  9  9 

X  F\  wild-type  cf  cT. 


-Forked  bristles. 


Reference. 

Wild- 
type 
99. 

Non-cross-over  cTcf. 

Cross-over  cTcf- 

Total 

Cross- 
over 
values. 

Vermilion 
forked. 

Wild- 
type. 

Vermilion. 

Forked. 

9I 

Ill 

Total . 

366 
376 

113 
1x6 

123 
ISO 

49 
42 

41 
3J 

326 
339 

28 
22 

742 

229 

273 

91 

72 

66s 

25 

In  table  39  vermilion  forked  and  wild-type  are  non-cross-overs,  and 
vermilion  and  forked  are  cross-overs,  giving  a  cross-over  value  ot  25 
units.  The  locus,  therefore,  is  25  units  to  the  right  or  to  the  left  of 
vermilion,  that  is,  either  about  58  or  8  units  from  the  yellow  locus. 

linkage  of  cherry  and  forked. 

Forked  males  were  crossed  to  cherry  females  (cherry  has  the  same 
locus  as  white,  which  is  about  i  unit  from  yellow)  and  gave  wild-type 
females  and  cherry  males.  These  gave  in  Fo  the  results  shown  in 
table  40.  The  non-cross-overs  (cherry  and  forked)  plus  the  cross-overs 
(cherry  forked  and  wild  type)  divided  into  the  cross-overs  give  a  cross- 
over value  of  46  units,  which  shows  that  the  locus  lies  to  the  right  of 
vermilion,  because  if  it  had  been  to  the  left,  the  value  would  have  been 
8  (z.  e.,  33-25)  instead  of  33  +  25  =  58.      The  difference  between  58 


6o 


SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 


and  46  is  due  to  the  expected  amount  of  double  crossing-over.  In  fact, 
for  a  distance  as  long  as  58  an  almost  independent  behavior  of  linked 
gens  is  to  be  expected. 

Table  40.— Pi  f/z^rry  9  9   X  forked  d^d".    Fi  wild-type  9  9  XFi  cherry  cfd". 


Reference. 

Females. 

Non-cross-over  d'  cT . 

Cross-over  cTcf . 

Total 

Cross- 
over 
values. 

Cherry. 

Wild- 
type. 

Cherry. 

Forked. 

Cherry 
forked. 

Wild- 
type. 

25 

25' 

36 

36' 

84 

84' 

85 

85' 

86 

87 

88 

Total . 

129 

167 

96 

57 

76 

62 

114 

98 
307 

351 
244 

145 

148 

88 

76 

86 

^6 

95 

323 

341 

246 

73 
74 

52 

41 
40 

24 

43 

48 

152 

183 

142 

70 

82 

52 

32 

34 

39 

78 

63 

144 

213 

142 

6S 
66 

35 
24 
38 

25 

41 

52 
Ii8 
160 
107 

68 
88 

51 

30 
26 
28 

53 
46 

165 

147 

104 

276 
310 
190 
127 
138 
116 

215 

209 

579 
703 

495 

48 
50 
45 
43 
46 
46 
44 
47 
49 
45 
43 

1,701 

1.705 

872 

949 

731 

806 

3.358 

46 

LINKAGE  OF  FORKED,  BAR,  AND  FUSED. 

This  value  of  58  gave  the  furthest  locus  to  the  right  obtained  up  to 
that  time,  since  forked  is  slightly  beyond  rudimentary.  Later,  the 
locus  for  bar-eye  was  found  still  farther  to  the  right,  and  the  locus  for 
fused  even  farther  to  the  right  than  bar.  A  cross  was  made  involving 
these  three  gens.  A  forked  (not-bar)  fused  male  was  bred  to  a 
(not-forked)  bar  (not-fused)  female  and  gave  bar  females  and  males. 
The  Fi  females  were  back-crossed  singly  to  forked  fused  males  with  the 
result  shown  in  table  41. 

Table  41.— Pi  bar9  9X  forked  fused  cf  cf .     B.  C.  Fi  bar  9 

X  forked  fused  cT  cf . 


Reference. 

f              fu 

B' 

f  B' 

'           fu 

B''f„ 

iA^ 

Total. 

Forked 
fused. 

Bar. 

Forked 
bar. 

Fused. 

Forked. 

Bar 

fused. 

Forked 
bar  fused. 

Wild- 
type. 

163 

164 

i6s 

II 

33 

Total. 

45 
71 
97 
21 

15 

55 

90 

106 

35 
23 

I 

4 
4 

2 

I 

2 
I 

4 
2 
I 

108 

166 

209 

59 

39 

250 

309 

I 

II 

10 

581 

NEW    DATA. 


6l 


The  same  three  points  were  combined  in  a  different  way,  namely,  by 
mating  forked  females  to  bar  fused  males.  The  bar  daughters  were 
back-crossed  to  forked  fused  males  and  gave  the  results  shown  in 
table  42. 

Table  4:2.— P^  forked  9  9   X  har  fused  d^cf .     B.  C.  F,  bar  9   X  forked 

fused  cf  cf . 


Reference. 

f 

B'f 

f,B'  U 

B'' 

f  B' 

Total. 

Forked. 

Fused 
bar. 

Forked 
bar  fused. 

Wild- 
type. 

Forked 
fused. 

Bar. 

Forked 
bar. 

Fused. 

158 

159 

160 

161 

162 

Total. 

131 

31 
29 
24 
96 

124 

45 

23 
II 
91 

I 

I 

2 

3 
I 
I 

3 
2 

I 

262 
76 

55 

36 

191 

311 

294 

4 

5 

6 

620 

By  combining  the  results  of  tables  41  and  42  data  are  obtained  for 
cross-over  values  from  which  (by  balancing  the  inviable  classes,  as 
explained  in  table  43)  the  element  of  inviability  is  reduced  to  a' mini- 
mum. 

Table  43, 


■ 

Total. 

Per  cent 

1,164 
96.9 

5 

0.42 

32 
2.7 

0 
0 

1,201 

The  linkages  involved  in  these  data  are  very  strong.  The  cross-overs 
between  forked  and  bar  number  only  5  in  a  total  of  1,201,  which  gives 
less  than  0.5  per  cent  of  crossing-over.  There  are  32  cross-overs  or 
2.7  per  cent  between  bar  and  fused.  The  value  for  forked  fused  is  the 
sum  of  the  two  other  values,  or  3.1  per  cent. 

LINKAGE  OF  SABLE,  RUDIMENTARY,  AND   FORK  ID. 

Rudimentary,  forked,  bar,  and  fused  form  a  rather  compact  group 
at  the  right  end  of  the  chromosome,  as  do  yellow,  lethal  i,  white, 
abnormal,  etc.,  at  the  zero  end.  The  following  two  cxpennu-nts  were 
made  to  determine  more  accurately  the  interval  between  rudmientary 
and  the  other  members  of  this  group.     A  sable  rudiiiuntary  forked 


62 


SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 


male  mated   to  a  wild   female  gave  wild-type  sons   and  daughters. 
These  inbred  give  the  results  shown  in  table  44. 

Table  44. — Pi  sable  rudimentary  forked  cf   X  wild  9  .     Fi  wild-type  9 

X  F\  wild-type  cT  &  • 


There  were  265  males,  of  which  42  were  cross-overs  between  sable 
and  rudimentary  and  4  between  rudimentary  and  forked.  The  values 
found  are:  sable  rudimentary,  16;  rudimentary  forked,  1.5;  sable 
forked,  17. 

LINKAGE  OF  RUDIMENTARY,  FORKED,  AND  BAR. 

The  three  gens,  rudimentary,  forked,  and  bar,  form  a  very  compact 
group.  A  rudimentary  forked  male  was  crossed  to  bar  females  and  the 
daughters  (bar)  were  back-crossed  singly  to  rudimentary  forked  males, 
the  results  being  shown  in  table  45. 


Table  45.- 


-Pi  rudimentary  forked  cf  X  bar  9  •     B.C.  Fi  bar  9 
X  rudimentary  forked  cf  cf  • 


Reference. 

r    f 

'■^ 

r  f|B' 

'f'fi' 

Rudi- 
mentary 
forked. 

Bar. 

Rudi- 
mentary 
bar. 

Forked. 

Rudi- 
mentary 
forked 
bar. 

Wild- 
type. 

Rudi- 
mentary. 

Forked 
bar. 

267 

268 

269 

Total. 

56 
82 
68 

104 
86 

lOI 

I 

2 

2 

I 

I 
I 

206 

291 

I 

4 

I 

2 

The  cross-over  values  are:  rudimentary  forked,  i;  forked  bar,  0.6; 
rudimentary  bar,  1.6.  The  order  of  factors  is  rudimentary,  forked, 
bar.     On  the  basis  of  the  total  data  the  locus  of  forked  is  at  56.5. 


NEW    DATA. 


63 


SHIFTED. 
Shifted  appeared  (January  1913)  in  a  stock  culture  of  vermilion  dot. 
The  chief  characteristic  of  this  mutant  is  that  the  third  lonj^itudinal 
vein  (see  text-fig.  f)  does  not  reach  the  margin  as  it  does  in  the  nor- 
mal fly.  The  vein  is  displaced  toward  the  fourth  throughout  its  length, 
and  only  very  rarely  does  it  extend  far  enough  to  join  the  marginal 
vein.  The  cross-vein  between  the  third  and  the  fourth  veins  is  often 
absent  because  of  the  shifting.  The  flies  themselves  are  smaller  than 
normal.  The  wings  are  held  out  from  the  body 
at  a  wide  angle.  The  two  posterior  bristles  of 
the  scutellum  are  much  reduced  in  size  and 
stick  straight  up — a  useful  landmark  by  which 
just-hatched  shifted  flies  may  be  recognized, 
even  though  the  wings  are  not  expanded. 

LINKAGE  OF  SHIFTED  AND  VERMILION. 

Since  shifted  arose  in  vermilion,  the  double 
recessive  shifted  vermilion  was  available  for 
the  following  linkage  experiment:  shifted  ver- 
milion males  by  wild  females  gave  wild-type 
males  and  females  which  inbred  gave  the  data 
shown  in  table  46. 

Disregarding  the  eye-color,  the  following 
is  a  summary  of  the  preceding  results:  wild- 
type?,  1,001;  wild-typed^,  437;  shifted  cf, 
328.  The  result  shows  that  shifted  is  a 
sex-linked  recessive.  The  data  of  table  46 
show  that  the  locus  of  shifted  lies  about  15 
units  on  one  side  or  the  other  of  vermilion,  fig.  f.— shiited  venation.    The 

1   •    ,  P  ,              ,       ,          1             .    •             c  third  longitudinal  vein  is  shitted 

which  from  the    calculated    position    Ot    Ver-  toward  the  fourth  and  fail!*  to 

milion  at  3'?  would  give  a  position  for  shifted  reach  the  margin.     Cros.^-vcin 

.    ,          "^^  r^   r  II  between  third  and  fourth  longi- 

at  either  18  or  48  trom  yellow. 


Table  46. — Pi  shifted  vermilion  cf  cf  X  ■'^ild  9  9 

X  Fi  wild-type  cf  cf . 


tudinal  veins  is  lacking. 
F,  uild-type  9 


Reference. 

Wild- 
type 

9  9. 

Non-cross-over  cTcf- 

Cross-over  cf  cT- 

Total 

Cross- 
over 
values. 

Shifted 
vermilion. 

Wild- 
type. 

Shifted. 

Vermilion. 

13 

29 

30 

31 

33 

34 

Total . 

345 
68 
191 
151 
133 
"3 

79 

20 

37 
41 
49 
56 

"5 

32 
54 
6S 
40 

59 

8 
3 
5 

17 
4 
9 

25 

4 
13 

>3 

6 

II 

227 

59 
109 
136 

99 
"35 

>5 
12 

17 

22 
10 

IS 

1,001 

282 

36s 

46 

7^ 

765 

>5 

64 


SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 


LINKAGE  OF  SHIFTED,  VERMILION,  AND  BAR. 

In  order  to  determine  on  which  side  of  vermiHon  shifted  lies,  a  shifted 
vermilion  (not-bar)  female  w^as  crossed  to  a  (not-shifted  red)  bar  male. 
Three  factors  are  involved,  of  which  one,  bar,  is  dominant.  The 
shifted  vermilion  (not-bar)  stock  is  a  triple  recessive,  and  a  three-point 
back-cross  was  therefore  possible.  The  daughters  were  bar  and  the 
sons  were  shifted  vermilion  (the  triple  recessive).  Inbred  these  gave 
the  results  shown  in  table  46.  The  smallest  classes  (double  cross-overs) 
are  shifted  and  vermilion  bar,  which  places  shifted  to  the  left  of  ver- 
miHon at  approximately  17.8  units  from  yellow. 

Table  47. — Pi  shifted  vermilion  9    X  bar  d'd'.     Fi  bar  9    X  Fi  shifted 

vermilion  cf  cf. 


Sh   V 


B' 


Refer-  I 
ence.     Shifted  j 

ver-    jBar. 
i  milion. 


65.... i       56 


108 


Sh 


B' 


Shifted 
bar. 


iVep 
mil- 
ion. 


20 


Sh  v^B- 


Shifted 

ver-     Wild- 
milion 

bar. 


type. 


33 


Sh 


V  B' 


Ver- 
Shifted.  milion 
bar. 


Cross -over  values. 


Total. 


Shifted 

ver- 
milion. 


242 


Ver 

milion 

bar 


Shifted 
bar. 


18 


The  stock  of  shifted  has  been  thrown  away,  since  too  great  difficulty 
was  encountered  in  maintaining  it,  because,  apparently,  of  sterility  in 
the  females. 

LETHALS  SA  AND  SB. 

The  first  lethal  found  by  Miss  Rawls  was  in  a  stock  that  had  been 
bred  for  about  3  years.  While  there  was  no  a  priori  reason  that  could 
be  given  to  support  the  view  that  lethal  mutations  would  occur  more 
frequently  among  flies  inbred  in  confinement,  nevertheless  a  hundred 
females  from  each  of  several  newly  caught  and  from  each  of  several 
confined  stocks  were  examined  for  lethals  (Stark,  191 5).  No  lethals 
were  found  among  the  wild  stocks,  but  4  were  found  among  the  confined 
stocks.  Whether  this  difi^erence  is  significant  is  perhaps  open  to  ques- 
tion. The  first  lethal  was  found  in  January  1913,  in  a  stock  that  had 
been  caught  at  Falmouth,  Massachusetts,  in  1911,  and  had  been  inbred 
for  18  months,  i.  e.,  for  about  50  generations.  This  lethal,  lethal  say 
was  recessive  and  behaved  like  the  former  lethals,  being  transmitted 
by  half  the  females  and  causing  the  death  of  half  the  sons.  The  posi- 
tion of  this  lethal  in  the  X  chromosome  was  found  as  follows,  by  means 
of  the  cross-over  value  white  lethal  sa.  Lethal-bearing  females  were 
mated  to  white  males  and  the  lethal-bearing  daughters  were  again 
mated  to  white  males.  The  white  sons  (894)  were  non-cross-overs  and 
the  red  sons  (256)  were  cross-overs.     The  percentage  of  crossing-over 


NEW    DATA. 


is  22.2.  A  correction  of  0.4  unit  should  be  added  for  double  crossing- 
over,  indicating  that  the  locus  is  22.6  units  from  white,  or  at  23.7. 

When  the  work  on  lethal  sa  had  been  continued  for  3  months,  the 
second  lethal,  lethal  sb,  was  found  (April  191 3)  to  be  present  in  a  female 
which  was  already  heterozygous  for  lethal  sa.  It  is  probable  that  this 
second  lethal  arose  as  a  mutation  in  the  father,  and  that  a  sperm  whose 
X  carried  lethal  sb  fertilized  an  egg  whose  X  carried  lethal  sa.  As  in 
the  cases  of  lethals  i  and  la  and  lethals  3  and  3^7,  this  lethal,  lethal 
j-^,was  discovered  from  the  fact  that  only  a  very  few  sons  were  produced, 
there  being  82  daughters  and  only  3  sons.  If,  as  in  the  other  cases,  the 
number  of  daughters  is  taken  as  the  number  of  non-cross-overs  and 
twice  the  number  of  sons  as  the  cross-overs,  it  is  found  that  the  two 
lethals  are  about  7  units  apart.  Since  the  two  lethals  were  in  different 
X  chromosomes,  all  the  daughters  should  receive  one  or  the  other  lethal, 
except  in  those  few  cases  in  which  crossing  over  had  taken  place.  Of 
the  daughters  19  were  tested  and  every  one  was  found  to  carry  a  lethal. 
Again,  if  the  cross-over  values  of  the  lethals  with  some  other  character, 
such  as  white  eyes,  be  found  and  plotted,  the  curve  should  show  two 
modes  corresponding  to  the  two  lethals.  This  test  was  applied,  but 
the  curve  failed  to  show  two  modes  clearly,^  the  two  lethals  being  too 
close  together  to  be  differentiated  by  the  small  number  of  determina- 
tions that  were  made.  It  seems  probable  that  lethal  sa  and  lethal  sb 
are  about  5  units  apart. 

The  position  of  lethal  sb  was  accurately  found  by  continuing  the 
determinations  with  a  white  lethal  cross-over.  A  white  female  was 
found  which  had  only  one  of  the  two  lethals  and  the  linkage  of  this 
lethal  with  eosin  and  miniature  was  found  as  follows :  A  female  carrying 
white  and  lethal  in  one  chromosome  and  no  mutant  factor  in  the  homol- 
ogous chromosome  was  bred  to  an  eosin  miniature  male.  1  he  white 
eosin  daughters  carried  lethal,  and  their  sons  show  the  amount  of 
crossing-over  between  white  and  lethal  (15.6),  between  lethal  and  mini- 
ature (19.9),  and  between  white  and  miniature  (32.9).  I  he  data  on 
which  these  calculations  are  based  are  given  in  table  48. 

Table  48. — Data  on  the  linkage  of  zvhite,  lethal  sb,  and  miniature, 

from  Stark,  iQij. 


w^        m 

yv]  Isb 

W^          , 

w^.  Ish .  m 

Total. 

Cross-over  values. 

— 

W      Isb 

w         m 

w    Isb '  m 

w 

Eosin 
miiii.iture. 

White 
miniature. 

Eosin. 

White. 

White      Lethal  sb  '     White 
lethal  J*,   miniature,   miniature. 

2,421 

524                 685 

48 

3.678 

1 
15.6     1       199             329 

iThe  curve  published  by  Miss  Stark  included  by  mistake  6  cultures  from  the  succo<-<linK  Rf"- 
erations,  and  these  coming  from  only  one  of  the  lethals  (lethal  sh)  increase  its  mod.-  so  th.it  the 
mode  of  the  other  lethal  (lethal  sa)  becomes  submerged.  If  these  cultnn-i  are  taken  <.ut  tlie 
curve  shows  two  modes  more  clearly. 


66  SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 

The  locus  of  this  lethal  is  at  16.7;  the  locus  of  lethal  sa  was  found 
to  be  at  23.7,  so  that  the  lethal  at  16.7  is  evidently  the  second  lethal  or 
lethal  sh  whose  advent  gave  rise  to  the  high  sex-ratio.  This  interpre- 
tation is  in  accord  with  the  curve  which  Miss  Stark  published,  for 
although  the  mode  which  corresponds  to  lethal  sa  is  weak,  the  mode 
at  15-16  is  well  marked. 

The  two  other  lethals,  lethals  sc  and  sd,  which  came  up  in  the  course 
of  these  experiments  by  Miss  Stark,  are  treated  in  other  sections  of  this 
paper. 

BAR. 

(Plate  II,  figures  12  and  13.) 

The  dominant  sex-linked  mutant  called  bar-eye  (formerly  called 
barred)  appeared  in  February  191 3  in  an  experiment  involving  rudi- 
mentary and  long-winged  flies  (Tice,  1914).  A  female  that  is  hetero- 
zygous for  bar  has  an  eye  that  is  intermediate  between  the  rounded  eye 
of  the  wild  fly  and  the  narrow  band  of  the  bar  stock.  This  hetero- 
zygous bar  female  is  always  readily  distinguishable  from  the  normal, 
but  can  not  always  be  separated  from  the  pure  bar.  Bar  is  therefore 
nearly  always  used  as  a  dominant  and  back-crosses  are  made  with 
normal  males. 

Bar  is  the  most  useful  sex-linked  character  so  far  discovered,  on 
account  of  its  dominance,  the  certainty  of  its  classification,  and  its 
position  near  the  right  end  of  the  X  chromosome.  The  locus  of  bar  at 
57  was  determined  on  the  basis  of  the  data  of  table  65. 

NOTCH. 

A  sex-linked  dominant  factor  that  brings  about  a  notch  at  the  ends 
of  the  w^ngs  appeared  in  March  1913,  and  has  been  described  and 
figured  by  Dexter  (1914,  p.  753,  and  fig.  13,  p.  730).  The  factor  acts 
as  a  lethal  for  the  male.  Consequently  a  female  heterozygous  for 
notch  bred  to  a  wild  male  gives  a  2  :  i  sex-ratio;  half  of  her  daughters 
are  notch  and  half  normal;  the  sons  are  only  normal.  The  actual  figures 
obtained  by  Dexter  were  235  notch  females,  270  normal  females,  and 
235  normal  males. 

The  location  of  notch  in  the  X  chromosome  was  not  determined  by 
Dexter,  but  the  mutant  has  appeared  anew  three  or  four  times  and  the 
position  has  been  found  by  Bridges  to  be  approximately  at  2.6. 


NEW    DATA. 


DEPRESSED. 


67 


Several  mutations  have  appeared  in  which  the  winj!,s  are  not  flat. 
Of  these  the  first  that  appeared  was  curved  (second  chromosome), 
in  which  the  wings  are  curved  downward  throughout  their  length,  but 
are  elevated  and  held  out  sidewise  from  the  body;  the  texture  is  thinner 
than  normal.  The  second  of  these  wing  mutants  to  appear  was  jaunty 
(second  chromosome),  in  which  the  wings  turn  up  sharply  at  the  tip; 
they  lie  in  the  normal  position.  The  third  mutant,  arc  (second  chro- 
mosome), has,  as  its  name  implies,  its  wings  curved  like  the  arc  of  a 
circle.  The  fourth  mutant,  bow  (first  chromosome,  fig.  c),  is  like 
arc,  but  the  amount  of  curvature  is  slightly  less.  The  fifth  mutant, 
depressed  (first  chromosome,  fig.  g),  has  the  tip  of  its  wings  turned 
down  instead  of  up,  as  in  jaunty,  but,  as  in  jaunty,  the  wing  is  straight, 
except  near  the  tip,  where  it  bends  suddenly.  Ihese  stocks  have  been 
kept  separate  since  their  origin,  and  flies  from  them  have  seldom  been 
crossed  to  each  other,  because  in  the  succeeding  generations  it  would 
be  almost  impossible  to  make  a  satisfactory  classification  of  the  various 
types.  But  that  they  are  genetically  difi^erent  mutations  is  at  once 
shown  on  crossing  any  two,  when  wild-type  oftsprmg  are  produced. 
For  instance,  bow  and  arc  are  the  two  most  nearly  alike.  Mated 
together  (bow  cf  by  arc  9  ),  they  give  in  Fi  straight-winged  flies  which 
inbred  give  in  F2  9  straight  to  7  not-straight  {i.  e.,  bow,  arc,  and  bow  arc 
together). 

Depressed  wings  first  appeared  (April  191 3)  among  the  males  of  a 
culture  of  black  flies.  They  were  mated  to  their  sisters  and  from 
subsequent  generations  both  males  and  females  with  depressed  wings 
were  obtained  which  gave  a  pure  stock.  This  new  character  proved 
to  be  another  sex-linked  recessive. 

LINKAGE  OF  DEPRESSKD  AND   BAR. 

Depressed  (not-bar)  males  mated  to  (not-depressed)  bar  females  gave 
bar  daughters.  Two  of  these  were  back-crossed  singly  to  depressed 
males  and  gave  the  results  shown  in  table  49.  Males  and  females  were 
not  separated,  since  they  should  give  the  same  result. 

Table  49.— Pi  depressed  9  9  X  bar  9  9  .     B.  C.  F,  bar  9  X  depressed  <?&. 


Non-cross-overs. 

Cross-overs. 

rotai. 

Cross-over 
values. 

Reference. 

Depressed. 

Bar. 

Depressed 
bar. 

Wild- 
type. 

4> 

70 

66  I 

67  I 

Total.. 

48 
85 

104 

21 
44 

161 

303 

39 
38 

133 

iSS 

65 

III 

464 

38 

68 


SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 


LINKAGE  OF  CHERRY,  DEPRESSED,  AND  VERMILION. 

The  linkage  value  38  (see  table  49)  indicates  that  depressed  is  some- 
where near  the  opposite  end  of  the  series  of  sex-linked  factors  from  bar. 
The  locus  could  be  more  accurately  determined  by  finding  the  link- 
age relations  of  depressed  with  gens  at  its  end  of  the  chromosome. 
Accordingly,  depressed  females  were  crossed  to  cherry  vermilion  males. 
Fi  gave  wild-type  females  and  depressed  males.  The  daughters  bred 
again  to  cherry  vermilion  males  gave  the  results  shown  in  table  50. 


Fig.  G. — Depressed  wing. 

The  data  only  suffice  to  show  that  the  locus  of  depressed  is  about 
midway  between  cherry  and  vermilion,  or  at  about  15  units  from  yellow. 

The  Fi  males  in  the  last  experiment  did  not  have  their  wings  as  much 
depressed  as  is  the  condition  in  stock  males,  and  in  Fo  most  of  the 
depressed  winged  males  were  of  the  Fi  type,  although  a  few  were  like 
those  of  stock.  This  result  suggests  that  the  stock  is  a  double  recessive, 
i.  e.,  one  that  contains,  in  addition  to  the  sex-linked  depressed,  an 
autosomal  factor  that  intensifies  the  effect  of  the  primary  sex-linked 
factor. 

Table  50. — P\  depressed  9  X  cherry  vermilion  d^cf  • 


First 
generation. 


Wild-;     De- 
type  pressed 

9  9.;  d^cf. 


21 


31 


Second  generation. 


Refer- 
ence. 


19  I 


y/c 


w^.d,, 


9  9  i  Cherry  j 

j    ver-    ' 
I  milion 


59 


23 


De- 
pressed 


24 


Cherry 

de- 
pressed 


Ver- 
milion 


W^ 


w'^dp^v 


!  De-  :^^/;7 

^•1  I  pressed  .  Wild 

Cherry  ]  "^  pressed 


cf. 


ver- 
milion 

6". 


ver- 
milion 


type 


NEW   DATA. 


CLUB. 


6y 


In  May  1913  there  were  observed  in  a  certain  stock  some  flies  which, 
although  mature,  did  not  unfold  their  wings  (text-fig.  Ha).  This  con- 
dition was  at  first  found  only  in  males  and  suspicion  was  aroused  that 
the  character  might  be  sex-linked.  When  these  males  were  bred  to 
wild  females  the  club-shaped  wings  reappeared  only  in  the  1%  males,  bur 
in  smaller  number  than  expected  for  a  recessive  sex-linked  character. 
The  result  led  to  the  further  suspicion  that  not  all  those  individuals  that 
are  genetically  club  show  club  somatically.  These  points  are  best  illus- 
trated and  proven  by  the  following  history  of  the  stock: 

Club  females  were  obtained  by  breeding  Fo  club  males  to  their  F2 
long-winged  sisters,  half  of  which  should  be  heterozygous  for  club. 


Fig.  H. — Club  wing,     a  shows  the  une.^panded  wings  of  club  flies;  c  shows  the  absence  oi  tlie  two 
large  bristles  from  the  side  of  the  thorax  present  in  the  normal  condition  of  the  wild.  b. 

When  the  F2  club  females  and  club  males  were  bred  together,  instead  of 
only  clubs  being  produced,  long-winged  flies  also  appeared.  In  fact, 
only  about  a  third  of  the  offspring  showed  the  club  character. 

Club  females  bred  to  wild  males  gave  some  club  males  in  I'l  (although 
most  of  the  males  had  long  wings),  and  in  Fo  some  of  the  females  and 
some  of  the  males  were  club.  In  all  essential  points  club  shows  the 
characteristic  features  of  a  sex-linked  recessive,  except  that  it  is  reahzt-d 
in  only  a  small  proportion  of  the  individuals  that  are  genetically  club. 

These  general  statements  are  substantiated  by  the  following  data: 
Club  male  by  wild  female  gave  in  20  F2  mass  cultures,  wild-type    Q  , 


JO  SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 

5,352;  wild-t\'pe  cf, 4,181;  club  cf ,  236.  The  wild-type  males  include, 
of  course,  those  club  males  that  have  expanded  wings  (potential  clubs). 

Club  females  by  wild  males  gave  in  the  F2  generation  (mass  cultures) : 
wild-type  9,  1,131;  wild-type  0^,897;  club  9,  57;  club  cf,  131. 

It  is  noticeable  that  there  were  fewer  club  females  than  club  males, 
equality  being  expected,  which  might  appear  to  indicate  that  the  club 
condition  is  more  often  realized  by  the  male  than  by  the  female,  but 
later  crosses  show  that  the  difference  here  is  not  a  constant  feature  of 
the  cross. 

Long-winged  males  from  club  stock  (potential  clubs)  bred  to  wild 
females  gave  in  Fo  the  following:  wild-type  9,  521;  wild-type  (and 
potential  club)  c:f,403;  club  6^,82. 

Club  females  by  club  males  of  club  stock  gave  in  F2:  potential  club  9  , 
126;  potential  club  cT,  78;  club  9,  95;  club  cf,  81.  These  results  are 
from  8  pairs.     The  high  proportion  of  club  is  noticeable. 

Potential  club  females  and  males  from  pure  club  stock  {i.  <?.,  stock 
derived  originally  from  a  pair  of  club)  gave  in  F2  the  following:  potential 
club   9,  1,049;  potential  club  cf ,  666;  club   9,450;  club  cf ,  453. 

GENOTYPIC  CLUB. 

Accurate  work  with  the  club  character  was  made  possible  by  the 
discovery  of  a  character  that  is  a  constant  index  of  the  presence  of 
homozjT^gous  club.  This  character  is  the  absence  of  the  two  large 
bristles  (text-fig.  hc)  that  are  present  on  each  side  of  the  thorax  of 
the  wild  fly  as  shown  in  figure  h^.  All  club  flies  are  now  classified  by 
this  character  and  no  attention  is  paid  to  whether  the  wings  remain 
as  pads  or  become  expanded. 

LINKAGE  OF  CLUB  AND  VERMILION. 

The  linkage  of  club  and  vermilion  is  shown  by  the  cultures  listed  in 

table  51,  which  were  obtained  as  controls  in  working  with  lethal  III. 

The  cross-over  value  is  shown  in  the  male  classes  by  the  cross-over 

r       •        276 

traction  — zr-  or  lo  per  cent. 
1463         ^  ^ 

LINKAGE  OF  YELLOW,  CLUB,  AND  VERMILION. 

The  data  just  given  in  table  50  show  that  club  is  19  units  from 
vermilion,  but  in  order  to  determine  in  which  direction  from  vermilion 
it  lies,  the  crossing-over  of  club  to  one  other  gen  must  be  tested. 
For  this  test  we  used  yellow,  which  lies  at  the  extreme  left  of  the  chro- 
mosome series.  At  the  same  time  we  included  vermilion,  so  that  a 
three-point  experiment  was  made. 

Females  that  were  (gray)  club  vermiHon  were  bred  to  yellow  (not- 
club  red)  and  gave  wild-type  daughters  and  club  vermilion  sons. 
These  inbred  gave  the  results  of  table  52. 

The  data  from  the  males  show  that  the  locus  of  club  is  about  midway 
between  yellow  and  vermilion.     This  conclusion  is  based  on  the  evi- 


NEW    DATA. 


71 


dence  that  yellow  and  club  give  18  per  cent  of  crossing-over,  club  and 
vermilion  20  per  cent,  and  yellow  and  vermilion  35  per  cent.  The 
double  cross-overs  on  this  view  are  yellow  club  (3)  and  vermilion  (3). 
The  females  furnish  additional  data  for  the  linkage  of  club  and  ver- 
milion. The  value  calculated  from  the  female  classes  alone  is  20  units, 
which  is  the  same  value  as  that  given  by  the  males. 

T.-\BLE  51. — Pi  club   9  9   X  vermilion  cf  cT.     Fi  zvild-type   9   X  f  1  club  d"  ■ 


Reference. 

Females. 

Non-cross-over  cT  cf . 

Cross-over  cfcT. 

Total 

Cross- 
over 
values. 

Club. 

Ver- 
milion. 

Club 
vermilion. 

Wild- 
type. 

137 

138 

139 

140 

144 

145 

146 

106 

107 

108 

109 

Total . 

75 
64 
56 
74 
97 
63 
126 
92 

55 
86 

103 
83 
77 
67 

126 

63 
114 

46 
III 

17 
24 
10 

13 

30 

'5 
44 

33 
31 
29 

25 
30 
18 
20 
32 
21 

45 
18 

35 

39 
32 
31 
39 
40 
29 
46 
34 
25 
32 
36 

34 
26 
21 
60 

28 

71 
18 

56 

6 

6 

4 

3 

10 

4 
9 
6 

7 
7 
4 
6 

7 
6 
15 
7 
9 
3 
6 

II 

8 
3 
5 

13 
6 

9 

10 

10 
9 
9 
8 

7 
13 
10 

7 
3 

7 

73 
70 
48 
60 
93 

54 
108 

83 
66 

78 
74 
79 
59 
54 

120 
66 

132 
42 

104 

23 
20 

«S 
13 

25 
«9 
15 
19 
'5 
22 
18 
19 
25 
24 
23 
26 
12 
14 
13 

1,578 

490 

697 

125 

151 

'.463 

>9 

Table  52. — Pi  club  vermilion  9  9  X   yellow  cTcf.     fi  'icild-type  9  9 

X  F\  club  vermilion  cf  cf  • 


F2  females. 

Fj  males. 

Non-cross-  i„ 

y 

y.ci 

V            V 

V 

1 

:  Cross 

-overs. 

H — 

•+- 

=H- 

~^ — 

Refer- 
ence. 

overs. 

Ci    V 

c 

V 

Club 
ver- 

1 

wiid-iciub. 

Ver- 

Yellow. 

Club 
ver- 

Yellow 
club 

Wild- 

Yellow 
ver- 

Club. 

Yellow 
club. 

Ver- 
milion. 

milion. 

type. 

milion. 

milion. 

ver- 

^P^i  milion. 

milion. 

i 

99   ••• 

44 

52 

13 

7 

35 

27 

2 

9 

8 

II 

0 

I 

ICXD.  .  .  . 

38 

58  i      6 

12 

43         23 

I 

IS 

" 

14 

0 

0 

lOI. . . . 

30 

32         6 

12 

19 

24 

6 

5         «o 

3 

I 

0 

102. .. . 

44 

55  ,     20 

13 

48 

38 

12 

14 

8 

IS 

I 

1 

103. . . . 

Total. 

.... 

43 

32 

7 

16 

13 

7 

I 

I 

156 

197  1    45 

44 

188 

144 

28 

59         50 

50 

3     ! 

3 

72 


SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 


LINKAGE  OF  CHERRY,  CLUB,  AND  VERMILION. 

The  need  for  a  readily  workable  character  whose  gen  should  lie  in 
the  long  space  between  cherry  and  vermilion  has  long  been  felt. 
Cherry  and  vermilion  are  so  far  apart  that  there  must  be  considerable 
double  crossing-over  between  them.  But  with  no  favorably  placed 
character  which  is  at  the  same  time  viable  and  clearly  and  rapidly 
distinguishable,  we  were  unable  to  find  the  exact  amount  of  double 
crossmg-over,  and  hence  could  not  make  a  proper  correction  in  plotting 
the  chromosome.  Club  occupies  just  this  favorable  position  nearly 
midway  between  cherry  and  vermilion.  The  distances  from  cherry 
to  club  and  from  club  to  vermilion  are  short  enough  so  that  no  error 
would  be  introduced  if  we  ignored  the  small  amount  of  double  cross- 
ing-over within  each  of  these  distances. 

It  thus  becomes  important  to  know  very  exactly  the  cross-over 
values  for  cherry  club  and  club  vermilion.  The  experiment  has  the 
form  of  the  yellow  club  vermilion  cross  of  table  52,  except  that  cherry 
is  used  instead  of  yellow.  Cherry  is  better  than  yellow  because  it  is 
slightly  nearer  club  than  is  yellow  and  because  the  bristles  of  yellow 
flies  are  very  inconspicuous.  In  yellow  flies  the  bristles  on  the  side  of 
the  thorax  are  yellowish  brown  against  a  yellow  background,  while  in 
gray-bodied  flies  the  bristles  are  very  black  against  a  light  yellowish- 
gray  background. 

For  the  time  being  we  are  able  to  present  only  incomplete  results 
upon  this  cross.  In  the  first  experiment  cherry  females  were  crossed  to 
club  vermilion  males  and  the  wild-type  daughters  were  back-crossed  to 
cherry  club  vermilion,  which  triple  recessive  had  been  secured  for  this 
purpose.     Table  53  gives  the  results. 


Table  53. — Pi  cherry  9  9  X  club  vermilion  cf  cf.     B.  C.  Fi  wild-type  9 

X  cherry  club  vermilion  cf  cf. 


Refer- 
ence. 

W 

Ci   V 

W^    Ci  V 

w 

Ci 

■^ 

W'jCi 

V 

Total. 

Cross 

-over  values. 

Cherry. 

Club 
ver- 
milion. 

Cherry 
club 
ver- 
milion. 

Wild- 
type. 

Cherry 

ver- 
milion. 

Club. 

Cherry 
club. 

Ver- 
mil- 
ion. 

Cherry 
club. 

Club 
ver- 
milion. 

Cherry 

ver- 
milion. 

163.. 

68 

68 

4 

10 

21 

13 

I 

0 

I8S 

8 

19 

26 

164.. 

99 

67 

13 

21 

21 

12 

I 

0 

234 

IS 

IS 

29 

165.. 

23 

37 

9 

7 

IS 

2 

0 

2 

95 

19 

25 

35 

166.. 

107 

86 

14 

28 

31 

43 

3 

3 

315 

IS 

25 

37 

167.. 

42 

49 

7 

II 

12 

II 

2 

2 

136 

16 

20 

30 

168.. 
Total. 

40 

30 

6 

15 

16 

8 

0 

0 

115 

18 

21 

39 

379 

337 

53 

92 

116 

89 

7 

7 

1,080 

IS 

20 

32 

I 


NEW    DATA. 


73 


A  complementary  experiment  was  made  by  crossing  cherry  club 
vermilion  females  to  wild  males  and  inbreeding  the  Fi  in  pairs.  Table 
54  gives  the  results  of  this  cross. 

Table  54. — Pi  cherry  club  vermilion  cfcf'.      9  9  X  wild  (f<f. 
Fi  zcild-type  9  X  Fi  cherry  club  verinilion  cf  cf . 


W"   C\   V 


w- 


+ 


Ci    V 


Reference.  Cherry 
I   club 


ver- 
'milion. 


Wild- 
type. 


Club 
Cherry.!   ver- 
imilion 


Cherry 
club. 


W^  Ci 


W^         V 

I    I 


Ver- 
1- 


Cherry 
ver-    Club, 


mi 


ion.  milion. 


Total 


Cherry 
club. 


Cross- 


over values. 


Club  Cherry 
i  ver-  I   ver- 
milion, milion. 


i88 6o       76  12 

189 228  314  48 

197 68       81  23 

Total.  356  471  I  83 


8 

44 
13 


12 

50 

9 


29 
60 

22 


65 


71 


III 


I 

8 
o 


200 

753 
218 


II 
»3 

17 


22 
16 


30 
27 

3> 


1,171 


14 


17 


28 


The  combined  data  of  tables  53  and  54  give  14.2  as  the  value  for 
cherry  club.  All  the  data  thus  far  presented  upon  club  vermilion 
(886  cross-overs  in  a  total  of  4,681),  give  19.2  as  the  value  for  club 
vermilion.     The  locus  of  club  on  the  basis  of  the  total  data  available  is 

at  14.6. 

GREEN. 

In  May  1913  there  appeared  in  a  culture  of  flies  with  gray  body-color 
a  few  males  with  a  greenish-black  tinge  to  the  body  and  legs.  The 
trident  pattern  on  the  thorax,  which  is  almost  invisible  in  many  wild 
flies,  was  here  quite  marked.  A  green  male  was  mated  to  wild  females 
and  gave  in  F2  a  close  approach  to  a  2  :  i  :  i  ratio.  The  green  reap- 
peared only  in  the  F2  males,  but  the  separation  of  green  from  gray  was 
not  as  easy  or  complete  as  desirable.  From  subsequent  generations  a 
pure  stock  of  green  was  made.  A  green  female  by  wild  male  gave  138 
wild-type  females  and  127  males  which  were  greenish.  This  green 
color  varies  somewhat  in  depth,  so  that  some  of  these  Fi  males  could 
not  have  been  separated  with  certainty  from  a  mixed  culture  of  green 
and  gray  males. 

The  results  of  these  two  experiments  show  that  green  is  a  sex-linked 
melanistic  character  like  sable,  but  the  somatic  difference  produced  is 
much  less  than  in  the  case  of  sable,  so  that  the  new  mutation,  although 
genetically  definite,  is  of  little  practical  value.  We  have  found  several 
eye-colors  which  differed  from  the  red  color  of  the  wild  fly  by  very 
small  differences.  With  some  of  these  we  have  worked  successfully  by 
using  another  eye-color  as  a  developer.  For  example,  the  double  reces- 
sive vermilion  "clear"  is  far  more  easily  distinguished  from  vermilion 
than  is  clear  from  red.     But  it  is  no  small  task  to  make  up  the  stocks 


74 


SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 


necessary  for  such  a  special  study.  In  the  case  of  green  we  might 
perhaps  have  employed  a  similar  method,  performing  all  experiments 
with  a  common  difference  from  the  gray  in  all  flies  used. 

CHROME. 
In  a  stock  of  forked  fused  there  appeared,  September  15,  191 3, 
three  males  of  a  brownish-yellow  body-color.  They  were  uniform  in 
color,  w^ithout  any  of  the  abdominal  banding  so  striking  in  other  body- 
colors.  Even  the  tip  of  the  abdomen  lacked  the  heavy  pigmentation 
which  is  a  marked  secondary  sexual  character  of  the  male.  About  20 
or  more  of  these  males  appeared  in  the  same  culture.  This  appearance 
of  many  males  showing  a  mutant  character  and  the  non-appearance 
of  corresponding  females  is  usual  for  sex-linked  characters.  In  such 
cases  females  appear  in  the  next  generation,  as  they  did  in  this  case 
when  the  chrome  males  were  mated  to  their  sisters  in  mass  cultures. 
Since  both  females  and  males  of  chrome  were  on  hand,  it  should  have 
been  an  easy  matter  to  continue  the  stock,  but  many  matings  failed, 
and  it  was  necessary  to  resort  to  breeding  in  heterozygous  form.  The 
chrome,  however,  gradually  disappeared  from  the  stock.  Such  a 
difficult  sex-linked  mutation  as  this  could  be  successfully  handled 
(like  a  lethal)  if  it  could  be  mated  to  a  double  recessive  whose  members 
lie  one  on  each  side  of  the  mutant,  but  in  the  case  of  chrome  this  was 
not  attempted  soon  enough  to  save  the  stock. 

LETHAL  3. 
In  the  repetition  of  a  cross  between  a  white  miniature  male  and  a 
vermilion  pink  male  (December  1913),  the  F2  ratios  among  the  males 
were  seen  to  be  very  much  distorted  because  of  the  partial  absence  of 
certain  classes  (Morgan  1914c).  While  it  was  suspected  that  the 
disturbance  was  due  to  a  lethal,  the  data  were  useless  tor  determining 
the  position  of  such  a  lethal,  from  the  fact  that  more  than  one  mother 
had  been  used  in  each  culture.  From  an  F2  culture  that  gave  practi- 
cally a  2:1  sex-ratio,  vermilion  females  were  bred  to  club  males. 
Several  such  females  gave  sex-ratios.  Their  daughters  were  again 
mated  to  vermilion  males.  Half  of  these  daughters  gave  high  female 
sex-ratios  and  showed  the  linkage  relations  given  in  table  55. 

Table  55. — Liyikage  data  on  club,  lethal  3,  and  vermilion,  from  Morgan,  1914c, 


Females. 

Males. 

Cl 

I3     V 

Cljls      V 

C,              V 

V 

I3     ' 

Club. 

Wild-type. 

Club  vermilion. 

Vermilion. 

S88 

182 

28 

11 

I 

NEW    DATA. 


75 


Lethal  3  proved  to  lie  between  club  and  vermilion,  13  units  from 
club  and  5  from  vermilion.  The  same  locus  was  indicated  by  the  data 
from  the  cross  of  vermilion  lethal-hearing  females  by  eosin  miniature 
males.  The  complete  data  bearing  on  the  position  of  lethal  3  is  sum- 
marized in  table  56.     On  the  basis  of  this  data  lethal  3  is  located  at  26.5. 

Table  56. — Summary  of  linkage  data  on  lethal  3,  from  Morgan,  1014c. 


Gens. 

Total. 

Cross- 
overs. 

Cross-over 
values. 

Eosin  lethal  3 

1,327 
1,327 

3,374 
222 

877 
1,549 
1,481 

1,327 

268 

357 
967 

29 
161 
105 
138 

3« 

20.2 
27.0 
29.0 
13.0 
18.4 
6.8 

9  3 

2-3 

Eosin  vermilion 

Eosin  miniature 

Club  lethal  3 

Club  vermilion 

Lethal  3  vermilion 

Lethal  3  miniature 

Vermilion  miniature 

LETHAL  3a. 
In  January  1914  a  vermilion  female  from  a  lethal  3  culture  when 
bred  to  a  vermilion  male  gave  71  daughters  and  only  3  sons;  34  of  these 
daughters  were  tested,  and  every  one  of  them  gave  a  2  :  i  sex-rario. 
The  explanation  advanced  (Morgan  1914c)  was  that  the  mother  of  rhe 
high  ratio  was  heterozygous  for  lethal  3,  and  also  for  another  lethal 
that  had  arisen  by  mutation  in  the  X  chromosome  brought  in  by  the 
sperm.  On  this  interpretation  the  few  males  that  survived  were  those 
that  had  arisen  through  crossing-over.  The  rarity  of  the  sons  shows 
that  the  two  lethals  were  in  loci  near  together,  although  here  of  course 
in  different  chromosomes,  except  when  one  of  them  crossed  over  to  the 
other.  As  explained  in  the  section  on  lethal  i  and  \a  the  distance 
between  the  two  lethals  can  be  found  by  taking  twice  the  number  of  the 
surviving  males  (2-f3)  as  the  cross-overs  and  the  number  of  the  females 
as  the  non-cross-overs.  But  the  34  daughters  tested  were  also  non- 
cross-overs,  since  none  of  them  failed  to  carry  a  lethal.      The  fractions 

\ = give  t;.7  as  the  distance  between  the  lethals  in  question. 

71  +  34      105  ^        ^  ^ 

In  the  case  of  lethals  3  and  3^  another  test  was  applied  which  showed 
graphically  that  two  lethals  were  present.  Each  of  the  daughters 
tested  showed,  by  the  classes  of  her  sons,  the  amount  ot  crossing-over 
between  white  and  that  lethal  of  the  two  that  she  earned.  1  hese 
cross-over  values  were  plotted  and  gave  a  bi modal  curve  with  modes  7 
units  apart.  It  had  already  been  shown  that  the  locus  of  one  of  the 
two  lethals  was  at  26.5,  and  since  the  higher  of  the  two  modes  was  at 
about  23,  it  corresponds  to  lethal  3.  The  data  and  the  curve  show 
that  the  lethals  3  and  3a  are  about  7  units  apart,  /.  r.,  lethal  3  lies 
at  about  19.5. 


76 


SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 


LETHAL  lb. 

A  cross  between  yellow  white  males  and  abnormal  abdomen  females 
gave  (February  1914)  regular  results  in  10  Fo  cultures,  but  three 
cultures  gave  2  9  :  I  cf  sex-ratios  (Morgan,  1914^,  p.  92).  The  yellow 
white  class,  which  was  a  non-cross-over  class  in  these  10  cultures, 
had  disappeared  in  the  3  cultures.  Subsequent  work  gave  the  data 
summarized  in  table  57.  At  the  time  when  the  results  of  table  57  were 
obtained  it  did  not  seem  possible  that  two  different  lethals  could  be  pres- 
ent in  the  space  of  about  i  unit  between  yellow  and  white,  and  this  lethal 
was  thought  to  be  a  reappearance  of  lethal  i  (Morgan,  igiib,  p.  92). 
Since  then  a  large  number  of  lethals  have  arisen,  one  of  them  less  than 
0.1  unit  from  yellow,  and  at  least  one  other  mutation  has  taken  place 
between  yellow  and  white,  so  that  the  supposition  is  now  rather  that 
the  lethal  in  question  was  not  lethal  i.  Indeed,  the  linkage  data  show 
that  this  lethal,  which  may  be  called  lethal  lb,  lies  extraordinarily  close 
to  white,  for  the  distance  from  yellow  was  0.8  unit  and  of  white  from 
yellow  on  the  basis  of  the  same  data  0.8.  There  was  also  a  total 
absence  of  cross-overs  between  lethal  lb  and  white  in  the  total  of  846  flies 
which  could  have  shown  such  crossing-over.  On  the  basis  of  this 
linkage  data  alone  we  should  be  obliged  to  locate  lethal  lb  at  the  point 
at  which  white  itself  is  situated,  namely,  i.i,  but  on  a  priori  grounds  it 
seems  improbable  that  a  lethal  mutation  has  occurred  at  the  same  locus 
as  the  factor  for  white  eye-color.  Further  evidence  against  this  sup- 
position is  that  females  that  have  one  X  chromosome  with  both  yellow 
and  white  and  the  other  X  chromosome  with  yellow,  lethal,  and  white 
are  exactly  like  regular  stock  yellow  white  flies.  The  lethal  must  have 
appeared  in  a  chromosome  which  was  already  carrying  white  and  yet 
did  not  aff'ect  the  character  of  the  white.  We  prefer,  therefore,  to 
locate  lethal  ib  at  i . i  — . 

Table  57. — Summary  of  all  linkage  data  upon  lethal  ib,  from  Morgan,  igi4b. 


Gens. 

Total. 

Cross-overs. 

Cross-over 
values. 

Yellow  lethal  lb 

Yellow  white 

744 

2,787 
846 

6 

23 
0 

0.81 
0.82 
0.0 

Lethal  \b  white 

FACET. 

Several  autosomal  mutations  had  been  found  in  which  the  facets  of 
the  compound  eye  are  disarranged.  One  that  was  sex-linked  appeared 
in  February  1914.  Under  the  low  power  of  the  binocular  microscope 
the  facets  are  seen  to  be  irregular  in  arrangement,  instead  of  being 
arranged  in  a  strictly  regular  pattern.  The  ommatidia  are  more  nearly 
circular  than  hexagonal  in  outline,  and  are  variable  in  size,  some  being 
considerably  larger  than  normal.     The  large  ones  are  also  darker  than 


NEW    DATA. 


77 


the  smaller,  giving  a  blotched  appearance  to  the  eye.  The  short  hairs 
between  the  facets  point  in  all  directions  instead  of  radially,  as  in  the 
normal  eye.  The  irregular  reflection  breaks  up  the  dark  fleck  which  is 
characteristic  of  the  normal  eye.  The  shape  of  the  eye  diff"ers  some- 
what from  the  normal;  it  is  more  convex,  smaller,  and  is  encircled  by 
a  narrow  rim  destitute  of  ommatidia. 

Facet  arose  in  a  back-cross  to  test  the  independence  of  speck  (second 
chromosome)  and  maroon  (third  chromosome).  One  of  the  cultures 
produced,  among  the  first  males  to  hatch,  some  males  which  showed  the 
facet  disarrangement.  None  of  the  females  showed  this  character. 
The  complete  output  was  that  typical  of  a  female  heterozygous  for  a 
recessive  sex-linked  character:  not-facet  9  9  (2),  112;  not-facet  d^  cT 
(i),  57;  facet  cf  cf  (i),  51- 

Of  the  three  characters  which  were  shown  by  the  F2  males,  one,  facet, 
is  sex-linked,  another,  speck,  is  in  the  second  chromosome,  and  maroon 
is  in  the  third  chromosome.  All  eight  F2  classes  are  therefore  expected 
to  be  equal  in  size,  and  each  pair  of  characters  should  show  free  assort- 
ment, that  is,  50  per  cent.  The  assortment  value  for  facet  speck  is  48, 
for  speck  maroon  52,  and  for  facet  maroon  48,  as  calculated  from  the 
F2  males  of  table  58. 

Table  58.— Pi  speck  maroon  d"  X  zvild  9  9.     B.C.  F^  wild-type  9   X  speck 

maroon  cf . 


Refer- 
ence. 

F2  females.                                                           F2  males. 

Speck 
maroon. 

Wild-  „       , 

Ma- 
roon. 

Facet. 

Speck 
maroon. 

Facet 

speck 

maroon. 

Wild- 
type. 

1                                                 1 

I 

Facet    ,,       ,     Fecct    Ma- 
maroon.    '"^'"   ■  speck.;  roon. 

66.... 

31 

30  i     26 

1 
i 

14 

14          10 

1 
11          17         >-         17 

) 

LINKAGE  OF  FACET,  VERMILION,  AND  SABLE. 

In  order  to  determine  the  location  of  facet  in  the  first  chromosome, 
one  of  the  facet  males  which  appeared  in  culture  66  was  crossed  out  to 
vermilion  sable  females.  Three  of  the  wild-type  daughters  were  back- 
crossed  to  vermilion  sable  males.  The  females  of  the  next  generation 
should  give  data  upon  the  linkage  of  vermilion  and  sable  while  the 
males  should  show  the  Hnkage  of  all  three  gens,  facet,  vermilion,  and 
sable.     The  oflFspring  of  these  three  females  are  classified  in  table  59. 

The  cross-over  fraction  for  vermilion  sable  as  calculated  from  the 
females  is  to-  The  cross-over  value  corresponding  to  this  traction  is 
10  units,  which  v/as  the  value  found  in  the  more  extensive  experiments 
given  in  the  section  on  sable. 

It  will  be  noticed  that  the  results  in  the  males  of  culture  150  arc 
markedly  difl'erent  from  those  of  the  other  two  pairs.  W  hile  the  sable 
males  are  fully  represented,  their  opposite  classes,  the  gray  males,  are 


78 


SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 


entirely  absent.     This  result  is  due  to  a  lethal  factor,  lethal  5,  which 
appeared  in  this  culture  for  the  first  time. 

The  males  of  the  two  cultures  149  and  151  give  the  order  of  gens 
as  facet,  vermilion,  sable;  that  is,  facet  lies  to  the  left  of  vermiUon  and 
toward  yellow.  The  cross-over  values  are:  facet  vermilion  40;  vermil- 
ion sable  12;  facet  sable  42.  Since  yellow  and  vermilion  usually  give 
but  34  per  cent  of  crossing-over,  this  large  value  of  40  for  facet  ver- 
milion shows  that  facet  must  lie  verv  near  to  yellow. 


T.\BLE  59. — Pi  facet  &   X  verviilion  sable  9  9 

X  vermilion  sable  cf  d^. 


B.  C.  Fi  wild-type  9 


Fj  females. 

F2  males. 

Non-cross-     ^ 

Cross- 
overs.      1 

overs. 

fa 

V  S 

fa  1  V  S      1        fa 

■+5 

%- 

S 

Reference. 

1 

Ver- 
milion 
sable. 

Wild-   Ver- 
type.milion. 

Sable. 

Facet. 

Ver- 
milion 
sable. 

Facet 
ver- 
milion 
sable. 

Wild- 
type. 

Facet 
sable. 

Ver- 
milion. 

Facet 
ver- 
milion 

Sable. 

149 

16 

29         3 

3 

17 

10 

8 

12 

2 

2 

I 

ISO 

13 

17  1       2 

2 

10 

9 

I 

.  . 

151 

Total . 

37 

63         7 

2 

38 

23 

12 

26 

2 

8 

4 

I 

66 

1 
109  1     12 

8 

55 

43 

29     i     38         5 

8 

6 

2 

LINKAGE  OF  EOSIN,  FACET,  AND  VERMILION. 

In  order  to  obtain  more  accurate  information  on  the  location  of  facet, 
a  facet  male  was  mated  to  an  eosin  vermilion  female.  The  Fi  females 
were  mated  singly  to  wild  males  and  they  gave  the  results  shown  in 
table  60.  The  F2  females  were  not  counted,  since  they  do  not  furnish 
any  information.  The  evidence  of  table  60  places  facet  at  i.i  units  to 
the  right  of  eosin,  or  at  2.2. 

Table  60. — Pi  eosin  vermilion  9   X  facet  c^.     fi  tcild-type  9   X  "wild  cf- 


Refer- 
ence. 

w^- 

V 

\\\  fa 

w« 

1 

\^ 

".  fa  . 

\ 

Total. 

1 

-^ 

I 

fa 

V 

fa     V 

L.10SS-0VCI  vaiuci. 

1  Eosin 
ver- 
milion. 

Facet. 

Eosin 
facet. 

Ver- 
milion. 

„           Eosin 

^     .      ^^"'    facet 
Eosin.    ver-      ^^^_ 

""••'^"•milion. 

i 

Wild- 
type. 

Eosin 
facet. 

Facet 
ver- 
milion. 

Eosin 
ver- 
milion. 

512.. 

5I3-- 
514.. 
5I5-- 
S16.. 
S17.. 
518.. 

•  43 
.      28 

18 
18 

10 

■      24 

•  44 

43 
35 
31 
60 

31 

34 
38 

1 

I 

I 
2 

I 

13 
19 
17 
20 

7 
10 

23 

16 

5 
II 

15 
12 
12 

22 

• 
I 

116 
89 
78 

"3 
60 
80 

130 

.... 

Total 

■    185 

1                   i                                     1                   ! 

272          2    j      4       109        93     1     . .     1      I         666     1.05     30.5 

1 
31-3 

NEW    DATA.  70 

LETHAL  SC. 

The  third  of  the  lethals  which  Miss  Stark  found  (Stark,  1915)  while 
she  was  testing  the  relative  frequency  of  occurrence  of  lethals  in  fresh 
and  inbred  wild  stocks  arose  in  April  1914  in  stock  caught  in  1910. 
Females  heterozygous  for  this  lethal,  lethal  sc,  were  mated  to  white 
males  and  the  daughters  were  back-crossed  to  white  males.  Half  of 
the  daughters  gave  lethal  sex-ratio,  and  these  gave  1,405  cross-overs 
m  a  total  of  3,053  males,  from  which  the  amount  of  crossing-over 
between  white  and  lethal  sc  has  been  calculated  as  46  per  cent. 

By  reference  to  table  65  it  is  seen  that  white  and  bar  normally  give 
only  about  44  per  cent  of  crossing-over  in  a  two-locus  experiment; 
lethal  sc  then  is  expected  to  be  situated  at  least  as  far  to  the  right  as  bar. 
Females  heterozygous  for  lethal  sc  were  therefore  crossed  to  bar  males, 
and  their  daughters  were  tested.  The  lethal-bearing  daughters  gave 
144  cross-overs  in  a  total  of  1,734  males,  that  is,  bar  and  lethal  sc  gave 
8.3  per  cent  of  crossing-over.  Lethal  sc  therefore  lies  8.3  units  beyond 
bar  or  at  about  66.5.  The  cross-over  value  sable  lethal  sc  was  found 
to  be  23.5  (387  cross-overs  in  a  total  of  1,641  males)  which  places  the 
lethal  at  43+23.5,  or  at  66.5.  We  know  from  other  data  that  there 
is  enough  double  crossing-over  in  the  distance  which  gives  an  experi- 
mental value  of  23.5  per  cent,  so  that  the  true  distance  is  a  half  unit 
longer  or  the  locus  at  67.0  is  indicated  by  the  1,641  males  of  the  sable 
lethal  experiment.  In  a  distance  so  short  that  the  experimental  value 
is  only  8.3  per  cent  there  is,  as  far  as  we  have  been  able  to  determine, 
no  double  crossing-over  at  all,  or  at  most  an  amount  that  is  entirely 
negligible,  so  that  a  locus  at  57+8.3  or  65.3  is  indicated  by  the  1,734 
males  of  the  bar  lethal  experiment.  To  get  the  value  indicated  by  the 
total  data  the  cases  may  be  weighted,  that  is,  the  value  65.3  may  be 
multiplied  by  1,734,  '^^^  ^7-^  may  be  multiplied  by  1,641.  The  sum 
of  these  two  numbers  divided  by  the  sum  of  1,734  ''^^id  1,641  gives  66.2 
as  the  locus  indicated  by  all  the  data  available.  This  method  has 
been  used  in  every  case  where  more  than  one  experiment  furnishes  data 
upon  the  location  of  a  factor.  In  constructing  the  map  given  in 
diagram  I  rather  complex  balancings  were  necessary. 

LETHAL  SD. 

The  fourth  lethal  which  Miss  Stark  found  (May  191 4)  in  the  inbred 
stocks  of  Drosophila  has  not  been  located  by  means  of  linkage  experi- 
ments. It  is  interesting  in  that  the  males  which  receive  the  lethal 
factor  sometimes  live  long  enough  to  hatch.  These  males  are  ex- 
tremely feeble  and  never  live  more  than  two  days.  I  here  is,  as  far 
as  can  be  seen,  no  anatomical  defect  to  which  their  extreme  feebleness 
and  early  death  can  be  attributed. 


8o 


SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 


FURROWED. 

In  studying  the  effect  of  hybridization  upon  the  production  of 
mutations  in  Drosophila,  F.  N.  Duncan  found  a  sex-Unked  mutation 
which  he  called  "furrowed  eye"  (Duncan  191 5).  The  furrowed  flies 
are  characterized  by  a  foreshortening  of  the  head,  which  causes  the 
surface  of  the  eye  to  be  thrown  into  irregular  folds  with  furrows 
between.  The  spines  of  the  scutellum  are  stumpy,  a  character  which 
is  of  importance  in  classification,  since  quite  often  flies  occur  which 
have  no  noticeable  disturbance  of  the  eyes. 

The  locus  of  furrowed  was  determined  to  be  at  38.0  on  the  basis  of 
the  data  given  in  table  61. 


Table  61.- 

-Data 

on  the  lin 

kage  of  fu 

rrowed,  from  Duncan, 

1915- 

Gens. 

F2  males. 

Total. 

Cross-over  values. 

Eosin,  miniature, 
furrowed 

Furrowed,  sable, 
forked 

Vermilion,    fur- 
rowed,  bar. . . 

W^ 

m 

w",       f  w  w^  m  .  f  w 

"^1       1 

„          Minia-  „     . 
h-osm                hosm 

fw 

1 
m 

m  tw 

mmia- 
ture. 

fur-       *"^- 
rowed.  '''^'^■ 

142 

59 

4 

3 

208 

29.8 

304 

30.3 

fw 

fw.S            f 

fw                .f 

fw     s 

Fur- 
rowed 
sable. 

Sable 
forked. 

Fur- 
rowed 
forked. 

S       f 

s 

'        '      f 

166 

9 

31 

3 

209  I     5.7 

1 

16.3 

19. 1 

V 

B' 

1 

V    fw            V 

V  fw.B' 

Ver- 
milion 
fur- 
rowed. 

Fur- 
rowed 
bar. 

Ver- 
milion 
bar. 

fw 

B'       fw  B' 

188 

9                 43 

0 

240 

3-8 

21.6 

17.9 

ADDITIONAL  DATA   FOR  YELLOW.  WHITE.  VERMILION,  AND 

MINIATURE. 

Considerable  new  work  has  been  done  by  various  students  upon  the 
linkage  of  the  older  mutant  characters,  namely,  yellow,  white,  vermilion, 
and  miniature.  We  have  summarized  these  new  data,  and  they  give 
values  very  close  to  those  already  pubHshed.  We  have  included  in  the 
white  miniature  data  those  published  by  P.  W.  Whiting  (Whiting  1913). 


NEW    DATA. 


8l 


Table  62. — Data  upon  the  linkage  of  yellow,  white,  vermilion,  and  miniatu 

{contributed  by  students). 


re 


Gens. 

Non-cross 

-overs. 

Cross-overs. 

Total. 

Cross-over 
values. 

White  miniature 

W 

m 

^       I 

1 

m 

6,2I9» 

7,378 

3,754 

3,337 

20,688 

34  2 

Yellow  miniature 

Vermilion  miniature 

Yellow  white 

W 

m 

5!^-+- 

m 

1,651 

1,116 

671 

1,047 

4,485 

38.3 

y 

J— f- 

m 

m 

761 

923 

421 

653 

2,758 

39 

V 

m 

51— H 

m 

1,685 

1,460 

32 

36 

3,213 

2.1 

y 

w 

y       -H 

w 

1,600 

1,807 

10 

7 

3,424 

o-S 

Yellow  vermilion 

White  bar 

y 

V 

^               1 

V 

509 

587 

328 

284 

1,708 

35-8 

w 

B' 

'"      +- 

B' 

198 

272 

168 

166 

804 

42 

Bifid  rudimentary 

Rudimentary  forked 

bi 

r 

5l_h 

r 

142 

15 

12 

116 

285 

45 

r 

r— H 

f 

f 

73 

211 

4 

288 

I  4 

^The  figures  to  the  left  in  each  double  column  correspond  to  the  .symbols  above  the  hc.ivy  line. 
as,  in  the  first  example  6,219  white  miniature.  The  similar  figure  to  the  riRht  corrcsi>ond»  to  the 
symbol  below  the  heavy  line.  If  no  symbols  are  present  below,  as  in  the  first  example,  the  column 
to  the  right  should  be  read  wild-type. 


82 


SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 


NEW  DATA  CONTRIBUTED  BY  A.  H.  STURTEVANT  AND  H.  J.  MULLER. 

Data  from  several  experiments  upon  sex-linked  characters  described 
in  this  paper  have  been  contributed  by  Dr.  A.  H.  Sturtevant  and  Mr. 
H.  J.  Muller,  and  are  given  in  table  63. 

Table  63. — Data  contributed  by  A.  H.  Stiirievant  and  H.  J.  Muller. 


jens. 


Yellow  white  X  bifid 


Yellow  X  vermilion 
bar 


White  bifid  X  forked 


Vermilion  miniature 
X  sable 


Sable  rudimentary  X 
forked 


Classes. 


y  w 


bi 


W 


233     254 


vB' 


99      lOI 


w  bi 


84      77 


V  m 


152    III 


143    195 


y+Y_21 


60     ss 


w 


y  w   bi 


10 


y    ,B- 


49 


48 


vv  bi     f 


9        6     65 


V            S 
-+ 

m 


4        2 


i*— f 


26      27 


59 


V  m    s 


12 


s__^ 


w  bi 


y  V 

=H — I 


14 


w 


Vf 


V 

-H h- 

m  s 


+ — ^ 


r  f 


Total. 


506 


435     32 


Cross-over  values. 


Yellow 
white. 


0.6 


Yellow 

ver- 
milion 


306 


286 


398 


White 
bifid 


Ver- 
milion 
minia- 
ture 


2.1 


Sable 
rudi- 
men- 
tary. 


13-3 


White 
bifid. 


3-2 


Ver- 
milion 
bar 


28 


Bifid 
forked 


42 


Minia- 
ture 
sable. 


Rudi- 
men- 
tary 
forked 


Yellow 
bifid. 


3.8 


Yellow 
bar. 


49 


White 
forked. 


45 


Ver- 
milion 
sable. 


;.i 


Sable 
forked. 


15 


White  Bifid  X  Rudimentary. 


F2  females. 


w       bi 


w 


bi 


F2  males. 


wbi 


w        r 


wbi  r 


w 


+7— f 


bi'r 


Total 


Cross-over  values. 


White 
bifid. 


Bifid 
rudi- 
men- 
tary. 


White 
rudi- 
men- 
tary. 


228     335 


15         II 


150      66 


2      10 


29        135 


395 


3-8 


42.3 


445 


White  BifidX  Miniature  Rudimentary. 


w       bi 


w 


bi 


-H H- 


++ 


+-I-+ 


344 


31 


109 


58 


41 


NEW   DATA. 


83 


SUMMARY  OF  THE  PREVIOUSLY  DETERMINED  CROSS-OVER  VALUES. 

The  data  of  the  earHer  papers,  namely,  Dexter,  1912;  Morgan,  iQior, 
1911^,  1911/,  1912/,  1912^;  Morgan  and  Bridges,  1913;  Morgan  and 
Cattell,  1912  and  1913;  Safir,  1913;  Sturtevant,  1913  and  1915;  and 
Tice,  1914,  have  been  summarized  in  a  recent  paper  by  Sturtevant 
(Sturtevant,  191 5)  and  are  given  here  in  table  64.  Our  summary  com- 
bines three  summaries  of  Sturtevant,  viz,  that  of  single  crossing-over 
and  two  of  double  crossing-over. 

Table  64. — Previously  ptiblished  data  summarized  from  Sturtevant,  IQIS- 


Factors. 

Total. 

Cross-overs. 

Cross-over 
values. 

Yellow  white 

46,564 
10,603 

18,797 

2,563 

191 

15,257 

41,034 

5,847 

5,151 

5,329 

1,554 

7,514 

12,567 

3,112 

159 

498 

3,644 
6,440 

1,100 

88 

4,910 

13,513 

2,461 

2,267 

212 

376 

1,895 

2,236 

636 

7 

1.07 
33-4 
34-3 
42.9 
46.1 
32.1 
32.8 
42.1 
44.0 

4.0 
24.1 
25.2 
17.8 
20.4 

4  4 

Yellow  vermilion 

Yellow  miniature 

Yellow  rudimentary 

Yellow  bar 

White  vermilion 

White  miniature 

White  rudimentary 

White  bar 

Vermilion  miniature 

Vermilion  rudimentary.  .  . 
Vermilion  bar 

Miniature  rudimentary.  .  . 
Miniature  bar 

Rudimentary  bar 

84 


SEX-LINKED    INHERITANCE    IN    DROSOPHILA. 


SUMMARY  OF  ALL  DATA  UPON  LINKAGE  OF  GENS  IN  CHROMOSOME  I. 

In  table  65  all  data  so  far  secured  upon  the  sex-linked  characters  are 
summarized.  These  data  include  the  experiments  previously  pub- 
lished in  the  papers  given  in  the  bibliography  and  the  experiments 
given  here.  The  data  from  experiments  involving  three  or  more  loci 
are  calculated  separately  for  each  value  and  included  in  the  totals. 

Table  65. — A  summary  of  all  linkage  data  upon  chromosome  I. 


Gens. 


Yellow  lethal  1 

Yellow  lethalli.... 

Yellow  white 

Yellow  abnormal 

Yellow  bifid 

Yellow  club 

Yellow  vermilion. . . . 
Yellow  miniature.  .  . 

Yellow  sable 

Yellow  rudimentary. 

Yellow  bar 

Lethal  1  white 

Lethal  1  miniature.  . 

Lethal  \b  white 

White  facet 

White  abnormal.  . . . 

White  bifid 

White  lethal  2 

White  club 

White  lethal  sb 

White  lemon 

White  depressed . . . . 

White  lethal  sa 

White  vermilion.  .  . . 
White  reduplicated. , 
White  miniature.. .  . 

White  furrowed 

White  sable 

White  rudimentary. 

White  forked 

White  bar 

White  fused 

White  lethal  sc 

Facet  vermilion 

Facet  sable 

Bifid  vermilion 

Bifid  miniature.  . . .  , 
Bifid  rudimentary.., 

Bifid  forked 

Lethal  2  vermilion. . 
Lethal  2  miniature.. 

Club  lethal  3 

Club  vermilion.  .  .  . , 
Lethal  sh  miniature. 
Lemon  vermilion 


Total. 


131 

744 
81,299 

15,314 

3,681 

525 

13,271 

21,686 

1,600 

2,563 
626 

1,763 

814 

846 

666 

16,300 

23,595 

8,011 

2,251 

3,678 

241 

59 

1,150 

27,962 

418 

[10,701 

208 

2,511 

6,461 
3,664 

5,955 
430 

3,053 
852 
186 

2,724 
219 
899 
306 

1,400 

6,752 
222 

5,558 

3,678 

241 


Cross-overs. 


I 

6 

87s 
299 
201 

93 
4,581 

7,559 

686 

1,100 

300 

7 

323 

0 

7 
277 
1,260 
767 
321 
572 

35 

12 

256 

8,532 

121 

31,071 

63 
1,032 

2,739 
1,676 
2,601 

186 
1,406 

278 
80 

849 
67 

384 
130 
248 

1,054 
29 

1,047 

733 

29 


Cross-over 
values. 


0.8 

0.8 

I.I 

2.0 

5-5 

17-7 

34-5 

34-3 

42.9 

42.9 

47-9 
0.4 

39-7 
0.0 

X.I 

1-7 
5-3 
9.6 

143 

IS. 6 

145 

20.3 

22.2 

30.5 
28.9 

33-2 

30.3 
41.2 
42.4 

45-7 
43.6 

43-3 
46.0 
32.6 
43-0 

311 

30.6 
42.7 
42.5 
17.7 

15-4 
13.0 
18.8 
19.9 
12.0 


NEW    DATA.  85 

Table  65. — A  summary  of  all  linkage  data  upon  chromosome  I — Continued. 


jens. 


Shifted  vermilion 

Shifted  bar 

Depressed  vermilion 

Depressed  bar 

Lethal  3  vermilion 

Lethal  3  miniature 

Vermilion  dot 

Vermilion  reduplicated.  . 

Vermilion  miniature 

Vermilion  furrowed 

Vermilion  sable 

Vermilion  rudimentary.  . 

Vermilion  forked 

Vermilion  bar 

Vermilion  fused 

Reduplicated  bar 

Miniature  furrowed 

Miniature  sable 

Miniature  rudimentary.  . 

Miniature  bar 

Furrowed  sable 

Furrowed  forked 

Furrowed  bar 

Sable  rudimentary 

Sable  forked 

Sable  bar 

Sable  lethal  sc 

Rudimentary  forked 

Rudimentary  bar 

Forked  bar 

Forked  fused 

Bar  fused 

Bar  lethal  sc 


Total. 

Cross-overs. 

1,007 

155 

242 

76 

59 

10 

464 

176 

1,549 

105 

1,481 

138 

57 

0 

667 

II 

10,155 

317 

240 

9 

9,209 

929 

1,554 

376 

66s 

163 

23,522 

5, 612 

9,252 

2,390 

583 

120 

208 

7 

1,855 

125 

12,786 

2,284 

3,112 

636 

209 

12 

209 

40 

240 

43 

663 

95 

872 

140 

7,524 

1,036 

1,641 

387 

1,456 

20 

664 

15 

1,706 

8 

1,201 

37 

8,768 

222 

1,734 

144 

Cross-over 
values. 


ISS 


31-4 

17.0 

38.0 

6.8 

9-3 

0.0 

17 

31 

3.8 

10. 1 

24.1 

24s 
23.9 
25-8 
20.6 


17-9 

20.5 

5-7 
19. 1 

17-9 

14  3 

16.0 

13.8 

23.6 

14 

2-3 

0.5 

31 

2.5 

8.3 


BIBLIOGRAPHY. 

Bridges,  Calvin  B. 

1913.  Non-disjunction  of  the  sex-chromosomes  of  Drosophtla.     Jour.  Exp.  Zool.,  15,  p.  587, 

Nov.  1913. 

1914.  Direct  proof  through  non-disjunction  that  the  sex-linked  gens  of  Drosophila  are  borne 

by  the  X  chromosome.     Science,  40,  p.  107,  July  17,  1914. 

1915.  A  linkage  variation  in  Drosophila.     Jour.  Exp.  Zool.,  19,  p.  i.     July  1915. 

1916.  Non-disjunction  as  proof  of  the  chromosome  theory  of  heredity.     First  instalment. 

Genetics  I,  p.  1-52;  second  instalment.  Genetics  I,  No.  2,  107-164. 
Chambers,  R. 

1914.     Linkage  of  the  factor  for  bifid  w^ing.     Biol.  Bull.  27,  p.  151,  Sept.  1914. 
Dexter,  John  S. 

1912.     On  coupling  of  certain  sex-linked  characters  in  Drosophila.     Biol.  Bull.  23,  p.  183, 
Aug.  1912. 

1914.  The  analysis  of  a  case  of  continuous  variation  in  Drosophila  by  a  study  of  its  linkage 

relations.     Am.  Nat.,  48,  p.  712,  Dec.  1914. 
Duncan,  F.  N. 

1915.  An  attempt  to  produce  mutations  through  hybridization.     Am.  Nat.,  49,  p.  575, 

Sept.  1915. 
HoGE,  M.  A. 

1915.     The  influence  of  temperature  on  the  development  of  a  Mendelian  character.     Jour. 

Exp.  Zool.,  18,  p.  241. 
Morgan,  T.  H. 

19103.     Hybridization  in  a  mutating  period  in  Drosophila.     Proc.  Soc.  Exp.  Biol,  and  Med., 

p.  160,  May  18,  1910. 
1910^.     Sex-limited  inheritance  in  Drosophila.     Science  32,  p.  120,  July  22,  1910. 
1910C.     The  method  of  inheritance  of  two  sex-limited  characters  in  the  same  animal.     Proc. 

Soc.  Exp.  Biol,  and  Med.,  8,  p.  17. 
19110.     An  alteration  of  the  sex-ratio  induced  by  hybridization.     Proc.  Soc.  Exp.  Biol,  and 

Med.,  8,  No.  3. 
1911^.     The  origin  of  nine  wing  mutations  in  Drosophila.     Science,  33,  p.  496,  Mar.  31,  1911. 
191  ic.     The  origin  of  five  mutations  in  eye-color  in  Drosophila^  and  their  mode  of  inheritance. 

Science,  April  7,  191 1,  33,  p.  534. 
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1911^.     Random  segregation  versus  coupling  in  Mendelian  inheritance.     Science,  34,  p.  384, 

Sept.  22,  1911. 
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inheritance  in  Drosophila.     Jour.  Exp.  Zool.,  11,  p.  365,  Nov.  191 1. 
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Exp.  Zool.  and  Med.,  9,  p.  73. 
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1914- 
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86 


BIBLIOGRAPHY.  87 

Morgan,  T.  H.,  and  C.  B.  Bridges. 

1913.     Dilution  effects  and  bicolorism  in  certain  eye-colors  ol Drosophila.     Jour.  Exp.  Zoo!., 
15,  p.  429,  Nov.  1913. 
Morgan,  T.  H.,  and  Eleth  Cattell. 

1912.  Data  for  the  study  of  sex-linked  inheritance  in  Drosophila.     Jour.  Exp.  Zool.,  July, 

1912. 

1913.  Additional  data  for  the  study  of  sex-linked  inheritance  in  Drosophila.     Jour.  Exp. 

Zool.,  Jan.  1913. 
Morgan,  T.  H.,  and  H.  Plough. 

1915.     The  appearance  of  known  mutations  in  other  mutant  stocks.     Am.  Nat.,  49,  p.  318, 

May  1915. 
Morgan,  Sturtevant,  Muller,  and   Bridges.     The    mechanism  of  Mendclian    heredity. 

Henry  Holt  &  Co.,  19x5. 
Morgan,  T.  H.,  and  S.  C.  Tice. 

1914.  The  influence  of  the  environment  on  the  size  of  the  expected  classes.     Biol.  Bull.,  26, 

p.  213,  Apr.  1914. 
Rawls,  Elizabeth. 

1913.     Sex-ratios  in  Drosophila  ampelophila.     Biol.  Bull.  24,  p.  115,  Jan.  1913. 
Safir,  S.  R. 

1913.     A  new  eye-color  mutation  in  Drosophila  and  its  mode  of  inheritance.     Biol.  Bull.  25, 
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Stark,  M.  B. 

1915.  The  occurrence  of  lethal  factors  in  inbred  and  wild  stocks  of  Drosophila.    Jour. 

Exp.  Zool.,  19,  p.  531-538.    Nov.  1915, 
Sturtevant,  A.  H. 

1913.  The  linear  arrangement  of  six  sex-linked  factors  in  Drosophila  as  shown  by  their 

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TicE,  S.  C. 

1914.  A  new  sex-linked  character  in  Drosophila.     Biol.  Bull.,  Apr.,  1914. 
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1913.     Viability  and  coupling  in  Drosophila.    Am.  Nat.,  47,  p.  508,  Aug.  1913. 


I     !l ^».< 


DESCRIPTIONS  OF  PLATES. 
Plate  I. 

Fig.  I.  Normal  9  • 

Fig.  2.  Sable  9  • 

Fig.  3.  Lemon  cf. 

Fig.  4.  Abnormal  abdomen  9  . 

Fig.  5.  Abnormal  abdomen  9 . 

Fig.  6.  Yellow  9 

Plate  II. 

Fig.    7.  Eosin,  miniature,  black  cT. 

Fig.    8.  Eosin,  miniature,  black  9  • 

Fig.    9.  Cherry. 

Fig.  10.  Vermilion. 

Fig.  II.  White. 

Fig.  12.  Bar  (from  above). 

Fig.  13.  Bar  (from  side). 

Fig.  14.  Spot  9   (abdomen  from  above). 

Fig.  15.  Spot  9   (abdomen  from  side). 

Fig.  16.  Spot  d^  (abdomen  from  above). 

Fig.  17.  Spot  c?  (abdomen  from  side). 


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E.    M     WALLACE     Ds 


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Plate  II 


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